Don't infringe copyrights. Articles should not be copied verbatim from Tibia.com or other fan sites. Try to always use original content!
Off-topic content. All content should be strictly about the MMORPG Tibia, which is run by CipSoft GmbH. Whilst it would be nice to have a wider range of diversity in what is allowed, this option is best in the long run.
Images. When uploading an image of an in-game object, use .gif. Also try to make sure your images are as compressed as possible without losing too much detail. One tool that helps with this is Adobe's ImageReady. Screenshots should be in .jpg. Filename extensions should always be in lower-case (.jpg not .JPG).
Accuracy. Only add information that is accurate, if you're unsure use a "?" or don't add it at all.
No Personal Articles Only add articles that are informative and people would benefit from reading. If you would like to write information about yourself and your own history, use your appropriate User: page. Also, don't pollute the global space (no Username redirect to User:Username). Famous Tibians are an exemption to this rule. Use your own judgment as to who would be considered famous, or ask a sysop. This rule also applies to guilds.
No Nonsensical Articles Articles should be strictly about actual in-game content; no nonsense made-up items should appear in the Wiki. When creating a new page, you should be able to authenticate your claim that the item actually exists, etc.
No Inciting Rule Violation Articles should not encourage in-game rule violations, mentioning them is fine provided it has a neutral or negative point of view. If in doubt, ask a sysop.
No Links to Illegal Sites Articles should not have links to sites which promote illegal content (cheats, OT etc.) or sites which are banned by tibia (like tibia.pl).