What I've learned looking back after a failed attempt, was all that pain I was feeling I simply transferred to the people I care about. I know that's what you want to hear, but it's what I've seen. Another is, you've talked yourself into this perspective "feeling" then you can talk yourself out of this feeling "depression". When ever you think of something negative, replace it with something positive. If you can't think of something, make something up (we all delude ourselves one way or another, it might as well be for your benefit). One of the harder parts I found is noticing when you're being negative, it's often very subtle. Dieting is a one example, when you hear someone say "they couldn't do a diet" undermining their confidence and making it vastly more difficult if they should try, if they got out of their own way it wouldn't be very difficult. I've taken it a bit further and told myself over an over feelings are just thoughts and I can think anything I want at anytime. Then I can think/feel what ever I want, when ever I want. It's just a thought, it's one of the easiest things to do, if it's difficult it's because you're making it difficult, get out of your way.
The more you practice the easier it gets, just like anything. And it really takes very little effort to accomplish.