Before a cell can be considered "done", it needs to at minimum satisfy the following criteria. Please make sure you go through this list for any cell you are working on or reviewing before sending it off to the next stage.
First right click the cell in the cell select window, and choose "Edit", and make sure the following steps all check out.
Location - Need to make sure the interior has its own location, instead of using an exterior location. Also need to make sure the location has the correct keywords. For example Ondi's Shack in Khuul is _KhuulOndisShackLocation
Acoustic space - use the appropriately named one for that interior type and the most appropriate size (01 being the smallest), this will be the default for that cell
Music - Make sure the cell has the correct music set. Dungeons have their own unique music tracks
Choose an appropriate image space for the interior ("_IS_InteriorGenericAncestralTomb" for example)
Choose an appropriate lighting template with the prefix _LT_ (For example "_LT_InteriorImperialShop"). Unless this cell is doing something unique, check all the checkboxes under "Lighting Template" on the "Lighting" tab. This is so that the information gets inherited from the template.
Cells with sky lights/holes need "show sky" checked under the lighting tab and their proper region selected. Do NOT check "Use Sky Lighting"
Make sure the owner NPC or faction is set, and if the area is a public place (such as a Temple) "Public Area" is checked.
Unless the cell author is going for something unique, the Directional Ambient Lighting settings should be inherited from the Lighting Template.
Natural lights, 'dust beam' lights, windows, and glow fills need their emittances set to the exterior (ex. "_FxBCSunlight" for dungeons in the Bitter Coast region)
If a light source doesn't seem to change with time of day in the CK, refresh the window with F5.
If the cell has a skyhole, add a trigger box for vampire sun damage (_dun_int_Vamp_SunSpot) where the light shines in. Do not add this for windows (assuming windows protect vampires from UV light?).
If a cell has different tilesets being used (for instance an Ancestral Tomb that has a cave section) make sure the interior has had roombounds created for it. If not, either create roombounds or send it back to Optimization with a note that the interior will need roombounds. Set each roombound's Image Space and Lighting Template to the appropriate settings (ie, a Daedric ruin with a cave section would have the Daedric ruin segment roombounds set to the Daedric template, while the caves would be set to the region-appropriate cave template).
Note that if a roombound does not have an explicitly set Image Space or Lighting Template then it will default to what is set in the cell properties. So for the above example you could set a given Daedric ruin's cell to the Daedric Ruin template, and just set the cavern roombounds to the cave template.
Make sure any light has a logical source, unless the light is intended to be a bounce light. For example, do not place a fire light in the middle of a hallway to brighten the area without a torch, candle, fire, etc. to accompany it.
Be careful with shadow casters, both because of the limited budget we have for shadow lights, but also because the shadows they cast are stark and can look funky when over a large enough area. Keep shadow casters, generally, to smaller areas.
Additionally, only 4 shadow casting lights will be rendered at a time, if more than 4 are on-screen at a time, only the 4 closest to the player will render. Keep to no more than 4 shadow casters per room.
To make sure you stay within the light limit, you can turn on a light debugging view.
Blues and greens indicate the surface is below the light limit
Purple means you are getting close
Red indicates the surface is at or above the limit. It will not guarantee there is flickering but care should be taken to lower the number of lights hitting a red surface
Set an acoustic space for the cell. Acoustic spaces have a number in their name that describes their size: 1 is small (fit for hallways and small rooms), 2 is average, and 3 is large (enormous rooms).
You may also place individual Acoustic Spaces to cover portions of the cell that don't match the default acoustic space (for example, a tomb that transitions into a cave). Place these very sparingly (~2-3 max), as the audio will subtly be interrupted any time the player moves between spaces.
Add sound markers where appropriate. What you use will depend on what the interior is.
For example, shacks might have creaking wood and trickling water underneath the shack
Dungeons, meanwhile, might have flowing waterfalls, or lava bubbling, or the hum of Dwemer machinery and lights
For big story moments, consider placing a music stinger. Please use these very sparingly; not every dungeon will warrant having a music stinger.
"Dread" is suited for quiet ominous moments.
"Reveal" is suited for entering a unique and extraordinary location.
"Reward" is suited for finding a very special item.
Interior matches the exterior, entrance matches exterior, load doors connected
Delete old dungeon layout if it still exists (Make sure you have markers turned on when you select the old layout, otherwise they won't be deleted with the rest of it)
Layout changes are permitted where needed, for example, lower class homes in Vivec City (canal level) should be small and cramped, not duplexes. Just be sure to update the navmesh when you make changes, or send back to navmesh with a note.
If hammocks are placed anywhere in the cell, mark them as "ignored by sandbox" if no one is ever scheduled to actually sleep on them or swap them with a bedroll or other sleeping arrangement otherwise. They do not have functioning sleep animations.
Use the Cell View window to ensure every mesh in the dungeon is using a Skywind model and prefix (_) in the editor ID (Markers and effects are ok)
For homes, research who the home belongs to, consider adding visual storytelling for their backstory if you want to add something to the cell.
Remove items that are illegal/contraband where necessary. Ordinary folk should not have moon dust, skooma, dwemer items, ebony, limeware, etc.
Remove any copies of the Lusty Argonian Maid. Also any other unique items, but especially the Lusty Argonian Maid.
Make sure books are relevant to their placement, an Imperial Fort is unlikely to have any Vivec sermons, for example.
If a book is marked "rare", there is a higher threshold to consider when using it. These might be books that are non-unique quest targets (eg, Vampires of Vvardenfell Vol II). Generally only use rare books if it was present in the same cell in the original game.
Older cells may contain copious amounts of tapestry. Although it can be fine for higher class homes, lower class homes should not have a ton of tapestries. Also try to limit tapestry variants to a minimum of 2 or 3. Same for cushions and such.
Avoid overuse of the paintings. Culturally they are Imperial and therefore should appear in Imperial-aligned locations such as forts or homes of non-Dunmer, or Imperialized Dunmer (House Hlaalu, basically). Additionally, these are expensive luxuries and would typically only appear in wealthy homes or forts, and even then be used sparingly except in the most wealthy of locations.
Homes should contain the basic necessities: food, clothing, a bedroom, a cooking/eating area, etc. lower class homes may use cooking stones rather than fireplaces, or no cooking instrument at all, etc. Basically, does the home or cell function as intended?
Try to keep furniture quality and style consistent. For example, upper class furniture probably wouldn't be paired with lower class furniture in the same room realistically. Also check that the correct furniture types are being used in the correct locations (wet textured furniture shouldn't be in well built homes, only in wet environments. Imperial furniture should only be used in imperial forts/settlements, etc.)
Home clutter should also reflect the economic class of the occupants; lower class homes should use redware dishes instead of silverware, should have fewer (if any) books, etc.
Most interiors were made before we had working weapon racks and mannequins. Be sure to replace any non-functional weapon racks you come across (prefabs found in zGWpnRacks).
If a piece of clutter is marked "UNIQUE" or "UNIQ" make sure that it is meant to be used in this location. If not, replace it with a non-unique piece or remove it entirely.
Place a COCMarkerHeading at the main entrance next to the teleportation marker
Set up all environmental hazards. For example, every fire that the player can step in needs to burn them. Process: select your object, such as a campfire, click T (trigger) and select a hazard, such as 0LSC_HazardTriggerFireLight. A triggerbox appears; open its properties and assign its linked ref as the first object you selected. Resize the proportions of the triggerbox appropriately. Making it a sphere is helpful for stuff like campfires
Ensure NorthMarker is actually facing north
Use Combat trigger boxes to make sure enemies do not engage with the player earlier than intended. More information can be found here under the section "How can I keep my NPCs out of combat?"
Add or remove idle markers where needed to create a sense of life and activity.
Add or remove FX markers where needed for things like dust beams, dust clouds, lava embers, heat shimmers, etc.
Check the location's wiki page to ensure the right NPCs are present. Sometimes NPCs can be placed in an exterior, however. Just make sure they're nearby
For generic enemies like undead, Daedra, and creatures use the "1_ENC_" Actors. Estimate a difficulty tier 1-5 so that it's relative to the dungeon type, the region it's located in, importance/quest-related, and other factors. For more info, click here for our creatures guide
Set the "Persistent Location" to the proper interior so AI packages function properly
For dungeons, have at least one NPC set as a Boss under "Location Ref Type". This makes it so an interior can be cleared. Often there is a quest with one of the enemies in the cell clearly indicated as the boss. Research the cell in the wiki to learn more about the context.
Place idle and patrol markers where appropriate. Ensure the proper NPCs are using them.
Set up proper NPC behavior packages and combat areas. More information can be found here.
You have some leeway on enemy size, if a monster needs to fit through a smaller space, you can adjust their size by no more than 10% in either direction. Any more or less than that and you will get strange behavior. And it just doesn't look great.
Make sure the dungeon is approachable by all play styles (Lines of sight/cover for rogues, ranged fights, etc.)
Also check that the dungeon flows well, there is a clear method to progress (even if the player lacks the tools/skills to do so at this time). The player should generally not have to backtrack, shouldn't easily get lost, and should not be able to go in circles.
Ensure that there are no pits or falls that the player can't get out of without relying on levitation.
Also ensure that there is no situation that the player can find themselves locked in a room. (Assume the player at any given point doesn't have mark/recall, has no intervention scrolls, cannot levitate, and has no lockpicks and no unlocking spells.)
Adjust any spots the player can get to that NPCs can't, to prevent the player from being able to cheese any encounters. If enemies have ranged attacks then it is acceptable.
Confirm that all traps are working and have proper scripts.
Traps should be telegraphed. We don't need traps explicitly pointed out, but consider how an entirely blind playthrough will experience the dungeon; reward careful and observant players. Subtle things like a small bloodstain near a trap that isn't obvious (for instance, daedric trap doors)