Avoid pop, juice and energy drinks - all high in sugar and/or HFCS - high fructose corn syrup (very bad - spikes insulin - causes weight gain). These are major players in weight gain. Also avoid junk foods, highly processed foods (comes in a box, bag or a can. Avoid White sugar, white flour, white rice (all highly processed food stuffs).
Take the stairs instead of elevators, walk briskly - do anything that makes you breath hard - this type of exercise raises your metabolism and has your muscles burn fat even while sleeping or sedentary.