Last summer I lost 30 pounds, going from 170 to 140lbs. This was after being overweight for most of my adult life. While I'm not an expert on weight loss, I do have a feel for what things worked (and continue to work for me):

1. Limit processed foods. That means anything from a box, package, wrapper, etc. (If you do eat some processed food, stick with items that have fewer than five ingredients - and be sure they're real ingredients, like "whole wheat" rather than "butylated hydroxytoluene".)

2. Eat whole foods. (The corollary to #1.) That means fruits, vegetables, salads and leafy greens, nuts, and beans. Things that come from nature, not from a manufacturer.

2. No dairy. That means no milk, yogurt, cheese, or ice cream. (Soy or almond milk is a good subsitute for dairy milk.) I realize there are conflicting stories on whether dairy is good or bad for the diet, but my personal experience is that it's bad and causes weight gain/retention. You might also want to read this book.

3. Cut back on meat. If you must eat meat, stick with fish or chicken/turkey - they're lighter and healthier for you anyway.

4. No sweets. That means cookies, candy, pastries, etc ... things with a lot of sugar in them. (Is sugar toxic?) If you need a sweet treat after dinner, eat fruit. Watermelon is wonderful in the summer. Berries (strawberries, raspberries, etc.) are good too. Try out different fruits and find the ones you like best.

5. No seconds. Stick with one serving of whatever you're eating. If you're not familiar with serving sizes, try measuring things out for a week or so. If you eat at a restaurant and they bring you a plate that's bigger than your head, cut everything in half. Take the rest home for later, or share it with a friend.

6. Eat low-fat. Nothing fried. Limit the oils, and try to use olive oil. If you eat salads, have the dressing on the side.

7. Exercise. Walking is good, easy, and free. Not only will it make weight loss easier, it'll make you healthier all around. (What is the single best thing we can do for our health?)

Here's some more great info: Top 15 Diet Hacks from Zen Habits.