A good thing to know about humour is that a person thinks something is funny when there are two contrasting or completely different emotions in one given situation, story or observation. It may seem far fetched at first, but when you think about funny stuff and search for contrasting emotions in it, you begin to see what I mean (by the way I myself didn't come up with that completely by myself). The sense of being superior to something or someone also initiates humour and laughter and a sudden understanding of things initiates laughter too - you know how sometimes you're studying something and you don't get it and then someone explains it to you and you suddenly realize that it's easy and you smile? That's also why jokes have a punchline - to build up contrasting emotions but keep them seperated and then combine those (by now stronger) emotions all at once with the punchline.
A nice and obvious example of this is the stand up comedy at the end of every Seinfeld episode - he takes something boring and ordinary from everyday life and then relates them with something different and extraordinary. And then usually acts out a situation involving all that stuff (like when he says how a nose job is called a rhinoplasty, which is kind of like comparing you to a rhino - isn't it bad enough that your nose is big as it is and they have to compare you to a rhino?)
There's also something about this on
howstuffworks.com.
I'd say just be confident about your sense of humour and observe everything that goes on around you carefully, you can make lots of funny remarks about that.
Another example from Seinfeld (although I don't think his jokes are really that ha-ha funny, because they are a bit obvious, but that's why they're a good example), I just found this on the net: What is a date really, but a job interview that lasts all night? The only difference is that in not many job interviews is there a chance you’ll wind up naked.
See, job interview - boring, naked or sex - not that boring, he combines those two and also has a kind of a punchline at the end which makes it more sudden and thus more funny.