Character biographies and histories are one of the main things readers look for on a wiki. Creating these is extremely important. It may be easier to start with characters who have appeared in fewer episodes.
Plot summaries are also searched for by users frequently. Plot summaries are aided by screenshots from the episode. Summarizing plots also makes writing character histories easier.
There are many locations in the series that have multiple appearances but don't have a page. Even just creating a page with a brief description and an infobox is extremely helpful.
Episode transcripts only receive a few readers, but they are still important resources. Completing these according to the Manual of Style is very helpful to the wiki.
Many crew members who work on the show do not have pages. If you see a red link to a person's name, consider starting an article.
Characters can use higher-quality images. Consider creating a render of a character. See Mortimor's render for an example. This is true to a somewhat lesser extent of object pages.
Many character galleries are blank or almost empty. Many episodes already have screenshots available; they just need the characters within them identified and placed on the proper page in the correct section.
There are some categories used for maintenance of this wiki. They should be empty, but they aren't always. Feel free to address some issues with pages in any subcategories of Category:Site maintenance.
We are all in this together. If you're new to this wiki, do not be overwhelmed. Just be yourself, and utilize what you have for the better of the community.