Going from a macro to a micro level, let's talk about how I've been changing my attitude.
I've struggled a lot lately with negativity and pessimism. My friend Ericka and a book about the plasticity of the brain helped me start on the road to a more optimistic self.
The basic trick is when you start having negative thoughts, try to think of something pleasant instead. I don't even always fully realize the pleasant thought. Often it is the thought of thinking of something pleasant that helps.
As another friend of mine pointed out, this does two things. It stops me focusing on the negativity, and it starts me focusing on something more positive.
This has been pretty successful so far. Ironically, some of the stressors I've had most recently have died down a bit as I've done this. But I think even if they flared up again I'd be a little better prepared to deal with them.