Here are some mistakes people commonly make on Wikia. Please try to avoid these!
Confusion about ownership
One of the great things about Wikia wikis are that they're based around the idea of community, where everyone has a hand in making decisions as a group. To that end, no single user owns a wiki, even if it was you that created the wiki or if you're an administrator. Wikis are owned by their communities, and everyone is welcome to edit and contribute.
The majority of pages on all Wikia should remain publicly editable, and are not to be protected. Pages may, however, be temporarily or permanently protected for legal reasons (for example, license texts should not be changed) or in cases of extreme vandalism or edit warring.
A wiki is a website anyone can edit. Sites on Wikia.com are examples of wikis. Wikipedia is a specific wiki at wikipedia.org and is not part of Wikia. You can call your site on wikia.com a wiki or a Wikia, but you cannot call it a Wikipedia. The word Wikipedia™ is a trademark.
Applying too many policies
It is not a good idea to try to enforce many policies on a new and small wiki. Some users make the mistake of trying to re-implement the numerous Wikipedia policies on a new wiki. Policies from wikis outside of Wikia do not necessarily apply here. Different Wikia will develop different policies over time. Things like vanity pages may be permitted by some Wikia and not by others. Instruction creep is another common mistake when making policies.
A page may be written poorly, yet still have a purpose. Consider what a sentence or paragraph tries to say. Clarify it instead of throwing it away. If the material seems wrongly categorized, or out of place, consider moving the wayward material to another page, or creating a new page for it. If you need to remove potentially useful content, it is usually best to move it to the discussion page. The author of the text once thought it valuable, so it is polite to preserve it for later discussion.
Deleting without announcing that you're doing it.
Remark on it in the edit summary box. Otherwise, other users who care about the page's development will be caught unaware, and may think you're being intentionally sneaky.
Deleting without justifying.
Deleting anything nontrivial requires some words of justification in the edit summary or on the discussion page.
If a page has been moved to a new title, an automatic redirect will be left from the old title to the new one. You should usually leave the redirect in place so people who have bookmarked or linked to the old title can easily find the new one.
Taking it too seriously
Wikis work through the collaboration of reasonable and consensus-oriented people. Flaming people and being rude is rarely acceptable on a wiki.
Don't get annoyed if you find some bad articles. Wikis are works in progress; please tolerate our imperfection, and help us improve. There are a lot of smart people editing Wikia sites, and everyone finds they have something to contribute. The best response to a bad page is to fix it!