There's no one straight answer to this. First of all, everyone's built differently, and as such, different exercises work best for different people, you need to find what works best for you. Furthermore, there's two types of exercise, anaerobic, which burns off fat and builds stamina, and anaerobic, which burns off fat and uses that energy to build muscle. Muscle weighs 2.94 times as much as fat, so when you first begin an anaerobic exercise regiment, you'll lose some weight as you burn off the fat, but then start gaining weight as you build up muscle. Aerobic exercises are like running and swimming, where anaerobic is things like weight lifting. You need to make your goal to shape your body how you want it to look, not to just drop weight, seeing as muscle weighs more than fat. You need to look at your body to determine which parts you want to shape, for example, if you have particularly fat arms, then you should probably do a pushup regiment (anaerobic) or shadow boxing (aerobic). Also remember, a good diet is very important, and it's not a matter of starving yourself, or only eating green foods or what not, but you need a balanced diet. You need to set a goal, work towards it, and have a well balanced diet. As for junk foods, when you feel like eating chips or whatever, try grabbing an apple instead.