Learning to manage one's emotions is, imo, one of the most important skills as a human, and it's sad that society hasn't taken enough time to really develop this skill, and to pass it on.
I find that it's not so much about control, and the best thing to do is getting in touch with your emotions. You try your best to remain your 'whole' self while experiencing and observing them, and doing so it's also easier to not get lost in them and do things that you wouldn't do unless you do.
A trick I use sometimes is if it seems like I need to 'rage' or anything, I do it in my imagination, cuz there there's no limit, I can express, and destroy stuff if I feel like it! And then in the real world, I don't get selfish (towards myself), I know I care about my environment (including others), so then I try to channel my willfulness into more constructive ways of going about things.
It's not always easy to do.. but it's like any skill, you get better at it.
Well, that's just some basics, but hopefully it can help you a bit. Still learning too..