I guess through good genes and a love of exercise I've never been overweight. Still weigh within 5 lbs of what I did in my early 20's.
I've known many people who were very overweight. The ones who successfully lost it did a few simple things:
-Drank LOTS of water. It not only flushes crud out of your system, but also decreases appetite because your stomach is fuller.
-Eat nutritious foods only. Empty calories taste good but don't do anything but fill the body with fat, salt, and tax the system
-Eat more slowly. It takes a few minutes for the brain to get an 'I"m full' signal. By eating more slowly (after a 16 oz. glass of water before every meal) you'll feel full when you're actually full, and not after you've already eaten too much.
-Exercise as you can. Start with walking a half a block. Increase as you feel better. Walking is the best exercise for losing fat. Running is for cardio. It does burn calories, but carbs rather than fat.
-Don't weigh yourself more than once a month. That way you'll get a better idea of how much progress you're making.
-Don't "Diet". Change eating habits. Things like apples, raw brocolli with Italian dressing, stuff like that to munch on at least gives you nutrition.
-All things in moderation.
-Take it a day at a time. The psychological defeat of 'giving up' leads to more overeating and a 'screw it' mentality.