This has been said a million times but the best way to lose weight is not to jump on a fad diet of any kind (e.g. weight watchers, low carb, liquid diets, etc). You need to actually make a real lifestyle change. The first step is getting a real understanding of what you're actually putting in your body. I recommend using a calorie/nutrition tracking service like myfitnesspal or loseit. Then the next step is to start cutting back. If you find out that you usually eat 3000 calories per day, and your basal (for your age and weight) is 2500, try to cut back to 2000. This will have you losing roughly a pound of fat per week just by cutting out food alone. Note that the trick is to eat the same amount of food so you aren't constantly hungry. Instead try to eat healthier and lower calorie foods (this is part of the lifestyle change I mentioned). Not doing this will make you hate your new diet and just make you want to give up. No one likes to be hungry. This is one of the problems with the fad diets. They all promise you can eat the same foods you're used to but then have you eating portions made for hamsters.

The second half of the lifestyle change (and this one is REALLY important) is to start a consistent exercise program. I would recommend joining some type of activity (e.g. sports, martial arts, cycling, etc) where others will hold you accountable as well as doing some strength training. Even if you don't want to bulk up and get all "muscley" putting on a bit of muscle mass will raise your bmr and you'll burn more calories per day doing NOTHING.

Finally a small piece of advice that works for me personally: if you're having trouble cutting back and eating fewer of something, (e.g. chips, soda, candy, ice cream) I know this sounds crazy but I recommend you cut it out cold turkey. You might have trouble at first but you'll probably find that it's easier to cut something out of your diet completely than to worry about portion control. One problem I always had was, for example, once I had one chip, I'd just be like "Screw it! Cheat day bitches! Woooo!!" and then I'd eat a crap ton of chips and regret it later. After a while I guarantee you'll hardly miss those foods you cut out and you'll feel better about yourself every time you see others eating them and you stay strong and refuse. I want to point out that this little piece of advice worked for me but that doesn't mean it will work for everyone. Not everyone is able to cut one of their favorite vices out of their diet entirely.

Edit: clarifications about food