1. Start a Food Journal -- if It's in Your Mouth It's on the Page
When something becomes a habit, you lose awareness of it. It's completely automatic. You regain awareness when you keep a food journal. Keep your food journal for a week, without changing your diet in any way. When you do this, you can see the habits which have caused you to put on weight in black and white.
Write down everything you eat and drink, and the hours at which you ate.
2. Move It! Get Moving Every Day
To stay healthy, you have to move. This doesn't mean that you need to spend an hour at the gym every day.
Start becoming aware of how much you sit down, and stand up more. At work, stand up when you answer the phone. Take the stairs. Walk to someone's office rather than sending them an instant message.
3. Shop Wisely - Eliminate Killer White Foods
Become aware of heavily processed foods -- those containing white flour, sugar and fat -- and work to eliminate them from your diet. Buy whole-meal bread. Eat fruit rather than a cookie or other processed snack.
4. Get a Diet Buddy -- Become Accountable
It's almost impossible to lose weight alone. Unless you have someone to check in with, you'll fall back into your bad food habits. Get a diet buddy, someone who has just as much weight to lose as you do, and who's eager to drop pounds.
Weigh yourself once a week. Your diet buddy does the same. When you know you'll have to share the weight you've gained with your diet buddy next week, you'll forgo that creamy dessert when you eat out.
5. Use Your Head -- Your Imagination Is Powerful
Here's a tip which really works: use your imagination to see yourself slim.
Daydream about that tiny bikini you'll fit into, and how great it will be to buy the clothes you really want. Your imagination is keeping you fat: you imagine how great a certain food will taste. Use your imagination to imagine how great you'll feel when you look slim and can do all the things you want to do.