I've just recently started (about 2.5 months back) getting "health serious". I've lost 15 pounds so far, putting me about 20 pounds over the max "ideal" weight range.

1. Use a good calorie tracker. Calorie trackers work, for many of us. My problem was I was making stupid decisions. For a 6'3" male of programmer's build (heh) to maintain 230 pounds static, you take in 2,800 calories every day. Anything less than that will cause you to lose weight. I set my target daily intake at 2000 calories, and have gone over that (although never over 2800) a few times in the past month or so.

2. Make sure you're getting the proper nutrition. The main hazard of "dieting" is that you don't take in enough nutrients. You do need fat and carbohydrates, despite popular diet myths; cut out the carbs and you will find your brain withering. One of my "hazard" nutrients is calcium: even at 2800 cals I was rarely getting enough in a day (and calcium needs to be spread out over the day as your body can only digest a certain amount of calcium and iron at a time). So, I pay particular attention to that nutrient. Getting the protein/carb/fat balance right is also critical (you should be getting a 50:30:20 mix of carb calories:protein cals:fat cals). To track nutrition you need to track more than calories or grams of fat or "weight watcher points". There's more than one or two dimensions which need to be tracked, at least at first in the "formative" stages of your diet change. YOU CAN LOSE A LOT OF WEIGHT AND END UP PERMANENTLY HARMING YOUR BODY. A lot of "fad" diets substitute nutrient-poor foods for nutrient-and-calorie-rich foods. These will bring your weight down, which is important if you are morbidly obese. It is not, however, worth permanently damaging your nervous system, heart, and lungs, to shed pounds a little faster.

3. Exercise! An hour of walking at a brisk pace burns about 400 calories. An hour of strolling burns over 250. You don't need equipment. You don't need preparation. Take your "decompression" time after the day while out walking and breathing in the smog ... er, fresh air. A nice side benefit is that you actually tend to see other people in your neighborhood! I am naturally quite exercise-averse. Still, I've found the walking routine has helped me in many ways. It's surprising how good it feels to complete a walk in record time or of record distance.

4. Weigh yourself at the SAME time of day on the same day of the week, weekly. Your weight will vary by a few pounds over the course of the day. Thus, if you weigh yourself in the morning one week and then the next week in the evening, you might see no improvement at all, while in reality you have made terrific improvement. Ideally, you'd weigh yourself multiple times during the day and take the minimum or average weight throughout the day as your weight that checkpoint. However, that takes time. Generally your lowest weight is in the morning, and so if you keep a schedule of weighing yourself in the morning then you should be able to track progress pretty well.

5. Remember that fat weighs less than muscle. If you find your weight not moving at all, but you are seeing improvement in your waistline, it is because you are gaining muscle faster than you are losing fat. That's good. Keep it up!

6. There are no "forbidden" foods. While tracking calories, you will find that you can't eat that huge slab of chocolate cake and make it through the rest of the day on the calories left in your budget. Still, you can allow yourself a portion of that cake if you "save" a little throughout the day (or week). Just like a household budget: never borrow forward, only pay forward. In other words, only eat that calorie-rich food *after* you've saved the equivalent calories from your day's or previous day's budget. Often, the key to staying within a healthy lifestyle is "giving in" to your cravings. If you cut out chocolate entirely, you're quite likely to backslide and binge on it a few days later. So, if choocolate is your thing, find a small-portion but satisfying source for it. Peanut butter is mine; I've found that Kraft's "South Beach" peanut butter cookies satisfy my craving for the flavor and keep me "on track" for the rest of the day.

7. Dietary change is hard. But, once you've made the change, keeping it is easier. Still, there are more days ahead of you than what you'll spend making the change, and slowly you will backslide if you don't keep periodic watch.

IMHO, all this is best done using a calorie tracker from a third party with a well-maintained database of foods. Yes, a "true" geek would build it themselves. But then, a "true" geek would probably spend a month getting their "system" up and running, have it "down" for maintenance every other week, and give up because it's all too much work two months in. You're already fighting inertia here. Don't give yourself another reason not to take control of your diet! It should take no more than 30 seconds to enter in the information on a meal, and you should be able to check on your overall nutrient consumption at any time.

I'm using "Calorie King", which is a pretty good program for tracking intake, exercise, and results. It has a rather exhaustive, well-maintained database, and cost $40 to register (only a one-week trial period, which IMHO is a bit insufficient). Every once in a while we'll eat something which isn't in the database, and it takes about a minute to enter a new food in. There are faults with the program (managing your own recipes is unintuitive and clunky, for instance), but, again: I'd rather spend my weeks making progress with a somewhat imperfect system than hold out for the perfect system.

Forgot to add: in order to make a 2000-calorie diet and remain satisfied, a large portion of your foods will necessarily become unprocessed and "healthy". Watching calories is not an alternative to eating "right"; it is a tool to get you to eat right without punishing your body and sending it into starvation mode.

@Matt:

Walking vs running: Those of us with bad joints need to choose the less jarring pace of walking over running. I'm not sure if your comments were aimed at me, but my point wasn't that walking is better than running or lifting weights or anything of the sort. My point is that walking is many times better than sitting on your butt. Like sitting on your butt: it requires no equipment. The only cost is the energy and commitment to getting up and moving.

If your time is too constrained, you can get just as much or more benefit from a half hour every other day of more strenuous activity. But, usually, then you are dealing with other expenses and hassles as well.

In any case, as that NY Times article shows, just adding exercise without monitoring (and, obviously, managing) your caloric intake is a fool's errand. Your body will naturally try to take in more energy to compensate for that which it expends. In that study, they saw a "statistically insignificant" 10% increase in caloric intake over the course of the exercise regimen; obviously that affects the effectiveness of the regimen!

As always, and moreso than most times, your mileage may vary. Every body responds differently to exercise. The only hard-and-fast rules are that you stick to a nutritionally sound program for more than a couple of months before trying something else, and that you avoid "cheating" the program. The program doesn't care if you cheat; you're only cheating yourself.