What are the best ways to lose weight?

Diet is key, even more important than exercise. I found that I can quickly lose body fat by making some very small changes:

Cutting out white bread and sugar. Cutting out sugar is tough at first but once you stick with it, you'll find that it becomes hard to eat things high in sugar as they'll taste overwhelming. I also find eliminating sugar means I never have severe hunger pangs, especially in the mornings.
Drinking lots of water. Your body can confuse hunger with dehydration. If you find yourself hungry for no good reason, try drinking water and waiting 20 minutes.
Don't eat late i.e. just before going to sleep. Try eating dinner at a reasonable hour.
Stick to lean meats, vegetables and fruit. You don't need to go crazy and treat this as a diet, it's remarkably easy to do unlike some fad cabbage soup diet.

As with everything, moderation is key. Having a chocolate bar one day isn't going to magically destroy all your progress but having ten of them will.