At its core, losing weight is a pretty simple matter of expending more energy than you take in.
Of course it's never that simple.
My biggest suggestion is to find something that gets your heart rate up around 120-145 beats per minute, and do that for at least thirty minutes, five times per week. This could be power walking, swimming, biking, jogging, inline skating, whatever.
Combine that with portion control. Keep in mind that what you're given as a meal at a restaurant is generally what a normal person would need for their total daily calorie intake. For a frame of reference, a single portion of meat should be about the size of a deck of cards.
I strongly recommend against any diets other than 'eat less, move more.' All my friends who have tried fad diets like atkins, south beach, etc, have eventually put the weight back on and more to boot. Weightwatchers seems to work for the people I know who've tried it, but that's probably because weight watchers is about portion control and not eating enormous amounts of calories.
A couple other tips:
- stop drinking soda
- don't drink more than one glass of juice a day - it's loaded with sugar
- chew your food more - it'll help you realize when you've eaten enough
- don't let yourself make excuses for giving in - most people fail at treating themselves 'just once'