Diet and exercise is key. If you dont have access to a gym try getting a hold of home workout programs like Insanity and P90x. I used insanity to shred 15 lbs before and is a good program if you stick with it.
If you dont feel like spending money for the programs you could try military type training which consists of Calisthenics and cardio. Push ups, abs ( sit up's flutter kicks, and mason twists), squats, lunges, planks and such. Do calisthenics for twenty minutes and then run for at least 30 mins. So about a 5k+ depending on how fast you are.
I also set workout goals when I worked out so that way I could keep pushing myself. It helped me stay motivated and not get bored and fall into monotiny.
You should lose a good amount of weight if your eating right and exercising. Eating right is also gonna be your key to maintaing you weight after the surgery. I weight 215lbs and shoot for 2000-2200 calories to maintain. At your weight you'd want to shoot for about 1700-1800 calories to lose weight and 2000 to maintain. Calorie counting works for me and I usually plan my meals for the week so that I can keep track of it.
As far as what I eat I dont really do anything crazy. I pratice portion control. I try to eat 5 servings of fruit and vegtables a day and I do the color thing with it. Like a variety carrots, brocolli, apples so I got the colors of orange, green, and red. I also snack on them instead of chips and cookies. I try not to buy chips and cookies so I have no choice but to snack on fruits and vegtables.
I try to get 10-15 grams of fiber daily. Most recommend 20, but it really upsets my gut when I try for that much. I recommend starting off slowly on the fiberous foods if your not used to it. It will wreak havoc on your gut if you try to eat to much to quickly.
This is what I used to lose 40lbs in about 3 months. I've always been a stocky kid and when I balloned up to 255 I had about enough. I'm at a healthy 215 right now and can probably lose 10 more lbs.
Good luck and you can PM me if you have any questions.