Taken from Theresa Duncan's blog Wit Of The Staircase
A great book to support one's wish to do this is Jack Canfield's How To Get From Where You Are To Where You Want To Be: The Success Principles (There's a link to success principles for adolescents as well).
I've read it and it's great. Full of success stories and commonsense ideas all with a good grounding in positive psychology. It's got all the visualization = attraction biznezz in it but it is very big on ACTION.
In other words, you can write positive affirmations till the cows come home (they are quite necessary) but you must DO whatever is necessary to achieve what you want.