Smaller portions was the key for me, since this October 07 i have lost 45lbs. I'm down to 225 with 25 more to go. I try to stay away from dairy as much as possible, but when i induldge i keep it to small portions.
You must exercise also, i hit the treadmill for about a half hour or go for a walk outside after dinner. You would be suprised how even a small workout has a big effect after a few months.
Try not to go to bed with a full stomach, i cant sleep with my stomach grumbling, so before i go to bed i will have a small snack, usually something fat/sugar free, depends on what you like.
Dont starve yourself...ive also found that once your body gets used to smaller portions, your stomach gets used to it and you still feel full.