Pretty much what insideontheoutside said - excellent tips!

I am pre-T but decided to start working out as I love the buzz you get from it and wanted to feel more confident. I work out at home and do quick, high-intensity bodyweight circuits of squats, press-ups, lunges, dips, sit-ups etc about 4 times a week. I've just started doing weights (with adjustable dumbbells), twice a week too as I want to increase my muscle mass now that my body fat has dropped to better levels.
My tip is to set yourself a goal and keep it simple and specific, e.g. "I want to drop an inch off my hips in a month." Take measurements of where you are now - weight, waist size, BMI, body fat % - and then you can compare where you get to in a month from now.
As for nutrition, try to up the protein content of your diet. You could have yoghurt instead of cake for dessert or scrambled eggs on brown toast instead of cereal for breakfast, just simple stuff like that. Don't cut out all your carbs or you'll feel pretty crap, but make sure the ones you do have are the more filling ones such as brown bread and wholegrain pasta. Protein shakes can be useful but if you want to buy one, check that it's a low-fat and low-carb one - I recommend MaxiMuscle ProMax or ProMax Diet.
And most importantly - have fun with it! Do exercises you enjoy and let yourself have beer and chips sometimes, cos man cannot live on salad alone!