20lbs is quite a large goal, and I don't suggest trying to lose that much that quickly. Healthily, you should be looking to lose about 2lbs a week, and the weight is unlikely to stay off if you go at a faster rate. However, if you are intent on losing more weight, I can only recommend that you remember to drink plenty of fluids, as well as listening to your body in order to make sure you're getting enough energy. If anything, cut back on sugary and processed foods, and if you're hungry between meals, eat some fruit or vegetables.