If you have never been good at strength training, you need to find things you like. Make certain decisions like, gym or home, or outdoors? What equipment to use? I would start out small by doing body weight exercises that work your whole body. A starter workout would be: Squats, lunges, push ups and crunches. Try to do 10 reps of each exercise, and you can repeat them for 1 to 3 sets total. Your legs have the biggest muscles in your body, so by building them up your will jump start your metabolism. Make sure you learn how to do them in proper form.