Sometimes it's just easier to act your way into better thinking than to think your way into better acting.

Act like a person who has self esteem, or at least, act like you think a person who has self esteem would act. Dress like them. Get your hair cut at their salon. Etc. But it's more than the looks--it's the daily acts that fill a life. If you HAD self-esteem, what would you do differently? Then do it.

It might take a while to stretch into a new life, but it's like yoga. Just keep doing it and the next thing you know, your hands are flat on the floor...