All these are very good tips, and of course Cheese has the best advise, but that only works in a perfect world, and in such a world no one would be fat anyway...
My $0.02:
If you are not really active, simply cut your portions at mealtimes. Don't eat until you are "full", and eat slower to boot. After a few days/weeks you body gets used to eating less and you aren't hungry all the time. It isn't difficult and no way I would call it a diet, because you still eat what you want. Just have one slice of pizza instead of two. Keep in mind I am talking NY pizza slices here. If it's from dominoes maybe go for 2 instead of 4.
And don't forget breakfast is basically a "free" meal. It is "free" because you body metabolizes stuff at max rate in the AM, when everything inside is getting up to speed. So the calories are used up at a much faster rate then.
Just lifting some light weights around the house can boost your metabolism, which helps you burn up the stuff that otherwise would park itself in your gut and stay there.