The first issue that most of my clients have in getting started is misguided focus. Those who are in the best shape are so because they are primarily focused on good health. The fit body naturally follows. That shift of consciousness is the first step towards achieving success.
More than likely, your current diet has caused you to feel fatigued and sluggish. This is the result of consuming foods that are high in calories but hold no nutritional value. Your body needs fuel. It needs nourishment and hydration in order to work properly. Without this, you are running on an empty tank. Ask yourself these two questions prior to eating or drinking anything: "Will this nourish my body?" and "How will I feel afterward?". Eat and drink for the purpose of good vibrant health. Let that be your drive and everything else will follow. Not only will you look better, but you will feel better too.
Tips: Ask your doctor about vitamin supplements. Vitamins are a good way to supplement the nutrition that your diet is lacking. Your main source of nutrition, however, should always be your diet.
Remember... focus first on good health and the rest will surely follow. Good luck!