Consider WHY you find things funny. Is it the way it's worded, is it funny to picture, etc.?
I have a decent sense of humor, I think, because my dad cracks jokes all the time, so I just kind of picked up on them. Maybe pay attention to the jokes/things your friends say that are funny and use their outlook on that situation in your own.
Try to be funny by pointing things out that seem funny about events instead of people, since you never know what will offend who.
Also, it's good to be able to laugh at yourself sometimes too. If you switched around some words in a sentence that made it funny, or tripped the other day, you can turn that into a humorous experience.
Try not to turn everything into a joke, especially things that really aren't funny. Be serious when you need to be. And don't laugh more than everyone else at your own jokes. That makes it seem like you think you're funnier than you are.
Don't force situations into a joke. Funny things almost always just HAPPEN. Don't go looking for the humor, let the humor come to you, haha

Hope I could help!