Sometimes, you may find something that may be suspicious to you that another user did, or the addition of inaccurate information on a page. This does not mean the user meant ill - they may not have known exactly what to do. In situations like these, you should assume good faith.
Tips for assuming good faith
If a user made a messy edit, help them out by cleaning it up. Messy edits =/= vandalism. Sometimes a user may not know how to edit properly, or factors such as Visual Editor can mess up the formatting. Instead of reverting and reporting, try helping and perhaps even leaving a message on their message wall.
If a user violates a rule, do not automatically assume it's a troll. New users do not always read the rules the first time they come to the wiki. Simply alert a moderator and they will most likely warn them in a timely manner. Do not treat new users as you would a vandal or troll, as this can make them feel unwelcome or confused.
Educate on the differences between fanon vs canon. Not everyone knows that certain elements of a character page or location can't just be edited with any information. A lot of users may think that this wiki is their free range to edit anything and do anything, when it is not. Instead of scolding them, try to give them tips on how to improve their edit.
Be a friendly and helpful face. New editors who make mistakes starting out may be intimated, as they are confused as to what to do and what policies they have to follow. If you were in their shoes, would you rather have users ganging up on you, or users helping you out? To be the latter helps grow our community and make it a friendlier place.