Don't drink soda, cut down on coffee if you're a drinker, and no more little debbie snacks. Try to eat several SMALL meals a day to keep your metabolism kicking in high gear.
What does your current exercise regimine look like right now? Be honest, it will benifit you, we don't care if you don't do a thing.
If your exercise routine is non-existant, then just do something. People make the biggest gains going from zero exercise to some exercise. Try to run 3 or 4 days a week, a slow jog will do. Pushups, chin ups, and crunches/pilates are good places to start in your home.