I used to be pretty big too, and I'm also not that tall. I've lost a good amount of weight (50lbs and hoping for more) and here's what worked for me.
1. Diet
I started to watch what I was eating and started to eat healthier too. I switched from regular pop to diet, started eating fruits and vegetables regularly, and avoided chips and cookies and other stuff of that nature. You can create a free account on something like to keep track of your daily calories. Most importantly, to lose weight you need to burn more calories than you take in.
2. Cardio
I basically did 20+ minutes of cardio 3-5 times per week. I started out easy and as I've lost weight I've increased the intensity and duration of my cardio sessions. I've mostly used the treadmill, stationary bike, and elliptical.
3. Weights
I starting regularly lifting weights and I documented what I was doing. I generally lift 3x's per week and do total body workouts each time. I find it to be really helpful when I go to the gym and know exactley what exercises I'm doing when I get there, and when I leave I write down what I did. Doing this allows me to track my progress and see my improvement.
4. Attitude
You have to want to become more fit and to lose the weight. At least for me, if I really want something then I'll work like crazy to get it, but if I don't want it badly enough then I can be lazy.
5. Tracking Progress
Whether you weigh yourself every day or only once per week, keep track of your weight loss.
This is just what has worked for me, take from it what you will.