I've spent most of my post-teenage life struggling with my weight. About 16 months ago, I made a fairly radical change to my eating habits and I've now lost 103 lbs.
There's two major things I changed about my diet. First, I ate less sugar. Second, I ate slower. Before I get into the details, I want to clarify something. I am a vegetarian now, but that's a decision unrelated to my attempt to lose weight. I lost over 60 lbs before I became a vegetarian. Vegetarianism wasn't a prerequisite.
Eat less sugar. That sounds pretty simple, doesn't it? Unfortunately, it was a lot harder than I thought it would be. A lot of preprocessed foods, including most bread you'll find in the super market, include superfluous high-fructose corn syrup. Even foods that market themselves as healthy will include copious amounts of sugar; they just cut out the fat instead. Unfortunately, that's the opposite of what my experience has taught me. I choose fat over sugar. My body can actually break down fat and do something useful it.
I found that once I reduced the amount of sugar I consumed drastically, my appetite became more regular and manageable. I get hungry again quickly when I have sugary food and it's usually accompanied by headaches, not by an empty stomach. I also have a harder time telling just how hungry I am when I've had much sugar. It scrambles my sense of what I need. I'm really vigilant now to check the labels of food I buy in the store. I also cook more of my own meals than I used to.
Fresh fruit is my one exception to the above rule. Fruit doesn't cause me any of the problems that, say, corn syrup laden bread does. I don't entirely understand why, but it seems to be broken down differently.
Eating slow was the other key change to my life style. If I wolf down my food, I can very easily eat more than I actually need without realizing it. I discovered that if I just slow down, take breaks, and take the radical step of chewing that I can actually tell when I've had enough food. I was never aware of the whole spectrum of sensations in my stomach until I slowed down and paid attention. I was amazed to discover that there's more than just "starving" and "stuffed".
Just these two things, I think, were the most important parts of my experience losing weight.