Eat often, but dont make it heavy with alot of bread or meat. Make it something light, like some fruit or a salad (Im serious!) Also, drink ALOT of water. Not only will it clean out your system, but it will make you healthier and when you are full on water, you dont eat as much. That also goes during meals; try to drink alot.
Do alot of cardio. These exercises take TIME, and if you want to burn fat, thats what you need to do. running, suicides (running suicides) stair climbing, breakdancing, all of that is good.
A few things to keep in mind. You never lose fat, the cells that store it only get smaller, like muscles. For each pound of fat there is something like 2000 calories in it. Which means if you want to lose a pound of fat, you need to have a DEFACITE of 2000 calories over some time. Lose that many calories too fast and you hurt yourself. There is no such thing as losing weight in a area by working that area, like getting rid of your gut by doing sit ups. It takes from fat over the whole body, so it takes some work if you got a little layer of fat on you :-P
The best way though, is to not lose weight persay, but to trade it for lean muscle. Do alot of cardio, but also follow it up with some workouts or burnouts. If you dont know what burnouts are, take 2 10 pound weights, and do 20 bicep curls, then 20 tricep curls. then 19 bicep curls, then 19 tricept and so on WITHOUT STOPPING! push yourself hard after your muscles get tired, rest for a little bit, and do it again. 3 sets of that. Its a awesome arm workout, and builds alot of endurance and muscle if you do it every other night.
One more thing, get on a body fat % calculator. Find out your percentage. 20-25 is usually good for the average person. If you want nice muscles and a defined 6 pack, you need to be down around 17-15 or lower. lover then say 5 and you are in trouble. (I know some swimmers who are around there) Im around 12% and i have a nice 6 pack, which is what you are looking for
If you want, there are a few exercises i do to keep my 6 pack.
with 20 lbs of weight on my sholders (usually in my hands) do 3 sets of 30, although you should prolly start around 15 X 3. Full body, which means put you legs up in the air, and pull your legs up higher when you pull you upper body up. Be careful though, if you do it wrong all you are doing is pulling your legs up and not working your abs at all.
Lie on your side, and raise it up. Do this 30 times, 3 times, on each side. This defines your sides, and makes it stand out more.
Do crunches for a set amount of time. My favorite thing to do is to put a song on, do crunches for the verse, and rest for the chorus, crunch for the verse, rest for the chorus. Gets kinda hard after a 5 minute song :-)
Do this EVERY DAY! Ones with weights, do every other day, but you can do the other ones every day, and its recommended you do.
Hope this helps
EDIT: also, keep in mind that these are what I do. If you need to, lower it to maybe 20 X 3 sets, or even 15X3. The first set should be kinda easy, the second set you should feel it not be as easy, and start to work your muscles, and your third set should be hard.