So here's the problem. You've found a fascinating wikia, just ripe for growth, and you're raring to go. But for some reason or other, it's not eligible for adoption. Maybe the admin is almost active and had edited in the last month. Or you haven't been on the wikia long enough to be eligible. Or maybe you just aren't ready to adopt yet.
But even without being an admin, there are lots of things you can do to help the wikia, and maybe get ready for adoption.
The first thing I would do is look to see who else is on the wikia. There are two good ways to do this. One is to go to Special:RecentChanges, your one-stop shop for wikia information. This is one of the most important pages on the wikia, and If you can master reading this, you will be a wiki expert in no time!
As well as showing you what edits have been made recently, Recent Changes will show you who is making those edits. It's often good to change the options to show more information, I usually select the last 500 edits in the last 30 days to get a really good view of the wikia's activity and health. You can also switch from "advanced" view (which condenses edits) to the full view in your preferences. I much prefer the full view.
The other tool is Special:ListUsers. This gives more specifics about the people on the wikia, both now and in the past. To see if there are any active admins and bureaucrats around, you can click "remove all" and then just check the two boxes for admins and bureaucrats. Remember that the default is for the tool to show people who have made 5 or more edits. So you may want to change that to "1 time or more" so you include anyone who has been active on the wikia
With these two tools you can really get a good idea of the wikias activity and community. Both pages also give you links to people's message walls - a great thing to use! Along with chat and the forum, message walls are a good way to introduce yourself and start conversations about how to improve the wikia. Do you want to improve the category system? Or maybe get more templates in place? On a very active and busy community, big changes are often hard to implement and require a lot of careful conversation. But a small or inactive wikia is more likely to welcome big changes and be ready for some new ideas.
So now you have a good idea of who is on the wikia, and have started making contact with anyone else who is active there. Or maybe you have found that there isn't anyone actively editing, just some drive-by traffic. What else can you do to help the wikia?
One useful thing is to patrol for bad edits. This is a time where Recent Changes comes in handy again. Special:WikiActivity is also useful to look at what's going on, and many find it easier to read. But remember that it won't show you all changes on the wikia - edits to many pages are hidden to show the most important. If you are patrolling for bad edits, you probably want to look at the larger picture.
There are many useful links on Recent Changes, and it's worth exploring them. One is the "diff". This shows you the difference between what was on the page before the edit and what is there after it. For forum and wall threads, click "hist" (history) instead, and you'll find any diffs for that thread there. On a diff, you can see two sides, the left shows the original page, and the right the change. You can compare the two and make sure the change is a valid one. You can also look directly on Recent Changes where the edit summaries may give you a good indication of whether the edit is good.
Now if the edit isn't good, then you don't need to be an admin to fix it! Let's look at a bad edit on an article.
The trick here is to look at the dates. Each links to a version of the page - nothing is lost! You can click the date of the good version, either on the history page or the diff, to view that version. Next, click "edit" while viewing that version, and then "publish" (without making any changes). And that's all there is to a manual rollback! The rollback and admin groups have a quick button that rollsback automatically, but even with that you sometimes need to do a manual rollback, so it's a good skill to have.
Other fixes you can do without admin rights including listing a page for deletion, blanking bad pages that don't have any good history, fixing typos and other errors from well meaning but untidy editors, and watching for conversations that might need another voice to help out.
But the biggest thing you can do for a small, inactive wikia, is add content! That's the number one task that will help the wiki revive. And you definitely don't need admin rights to do that.
Look at what topics have obvious holes. Think about what people are most likely to be looking for. Maybe that will be a summary of the plot for each episode. Or a really good article about the main character. Remember, you can gather information from anywhere, as long as you use that information to write your own original text.
Adding categories in a clear and organized way is another good way to help the wikia. That will improve search results and help people find similar articles.
And even if you can't change the theme or background yet, you can beautify the wikia with new images and videos. Visual media is a big draw for readers, and maybe some of those readers will be the next editors. Think about how you might use video or images to explain a skill, or to show a snippet of an episode to demonstrate a point. You can do a lot to make the wikia a more attractive place.
So as you can see, you don't need to be an admin to do good things for a small, quiet, or abandoned wikia. You can make a big difference, and help the wikia and the community grow and thrive.