Here's a tip: jokes that rely entirely on a character's action or posture (such as using frozen Brad to represent a person that apparently has been "blasted", as well as the kid who appears to be holding his balls (in "Prostitute Office")) do not work at all. Every concievable such joke has already been made to death and been done in much funnier ways. Like El_Phen said, look at the top-rated page and see how people craft truly funny comics.
However, even if you take this advice to heart, I still have my doubts that your comics are going to be funny any time soon. You're obviously a young kid and, no offense, but kids just aren't mature enough to be funny. When I was 10-15 or so, I was totally un-funny. I didn't make a single good joke during my puberty years, and neither has anyone else. Sorry, but that's just how it is. Maybe if you start smoking pot, you'll have a chance, but that would probably just result in horrendous pot-smoking-kid jokes, which are even worse than regular kid jokes.
Anyway, you can feel free to make all the comics you want for your own amusement or to show your friends or whatever, but don't expect anyone on this forum to like your comics for at least five more years.