I find that the times I actually make a joke (that is, put effort into being funny) I end up looking stupid.
First of all, know thyself. If you're funny, only make a joke if it is FUNNY WITHOUT EFFORT or humorous AND extremely clever/quick witted.
If you don't know what I am talking about above and/or wonder "gee, am I funny?" FOR GOD'S SAKE, leave the yuks to us professionals.
-NS