Alrighty, I've got-um some tips! :P

As far as discovering jokes to put in the comics, it gets easier as you go.

In case you have trouble:
Don't get discouraged, but if you do, don't give up. Presistance is important. Skill is like a muscle and develops as you work it. If you get to the point where you mess up like crazy and have worn the paper clean through with the earaser, that is the time to take a break and relax. There is kind of a "zone" in areas that require skill. There is stuff that can disrupt this "zone", and it is all in the mind. The right mindset makes a big difference. A steady hand is good, but the mind is where all the magic happens ^_^... And I'm not saying that you should meditate and do yoga, or anything.

In reguards to developing skill:
Just think like an experienced artist and cartoonist. Weather you are or you aren't, if you think like one, you will start to draw like one... I think. In other words, examine lots of other people's work, and imitate the ones you like, making sure not to completely rip off their work. And it'll make more sense. My skill improved the most drasticly when I was inspired by other people's work.

I hope this helps