How can i learn to be more laid back?

I wouldn't say i'm a particularly serious person in general, i can always laugh at myself when i do something stupid and i can let go and have fun but when it comes to certain things i'm just way too uptight about them. I worry far too much for starters, about things that shouldn't bother me, and i'm extremely sensitive too. I really want to be more laid back, but i don't know how? For example, if someone says something to me in harmless manor i will interpret it as being something bad, or get upset by it. My brother doesn't worry about anything ever, he's almost falling over backwards he's so laid back :P So basically, how can i because less tense and over emotional about everything and just relax? Thanks :)