Search Sanitization

I'm writing a *very* simple search form for my db and was interested in hearing some recommendations on what to check for with the user's input for the search. However, I guess more specifically my question is if anyone had any advice as to other things I should check since it's a search form. Obviously there's a lot more valid entries that a user can make than a normal form where you might know more specifically what they should enter and thus your validation can be more stringent. Any advice? Thanks!