I've tried reading a couple of books on being funny and they helped very little, if at all. They all basically say the same thing in a lengthy and unnecessary fashion so I'll try to sum up its most important parts while adding some things from my own personal experience. Humor basically comes down to status. David DeAngelo pointed it out in his ****y and funny program that if a high status male in a given group simply laughs for no reason, everyone within the group starts to smile and wonder what is so funny? Next thing they know they're sort of giggling and they don't know why. Since they follow under him, and he's the one laughing, in their minds they're thinking something has to be funny if the leader is laughing about it. Now if a low status male were to do the same, the others in the group would think he's a dork.
It all comes down to what the DJ bible has been teaching you; voice projection, tone, calmness, etc. Before I knew of all of this stuff, I would think of some artificial funny stories to make up before bedtime to share with my friends. In those moments of silence after a story was told or a short conversation has ended, I would very quickly before someone else says something, tell my story, only to have no one laugh. That's because I rushed it and had a weak voice. Now when I tell my stories, I speak with a confident, deep voice and simply take my time. Whenever someone tries to interrupt me, I simply ignore what they are saying and keep talking. That tells the group that what I'm saying is important.
Also, what a lot of people love doing is exaggerating and/or sugar coating their stories to make it seem more funny. I used to do this a lot when I was younger and it pissed off my cousin because he knew what I was doing. One of my friends does this and guess what? No one really laughs at his stories, even though they're a lot more comical than the stories I have to tell. I realized later on that nothing is funnier than the truth. My exaggerated and sugar coated stories sucked because they weren't funny for that very reason. Just stick with the entire truth, project them with a strong and calm voice and you'll become a funny guy.
For improb I saw a couple of seminars and they really didn't help. What helped me was watching a lot of comedies like Dave Chappelle, Chris Tucker, etc. It helps keeping up with pop culture. Also, the bulk of humor comes from the pain or suffering of others, so don't be afraid to make fun of your friends or other people you completely don't know. Often times when I'm in the car with my friends, I think of something funny to say about the random people in the streets. Just don't do it to the point you piss them off or seem insecure about it.