Diet is HUGE. It is just as important, if not more important, than exercise. Make sure you are eating as healthy as possible, eat smaller portions & try to get lots of protein to combine with your workouts if you are looking to bulk up with a bit of muscle. There are lots of great exercise diets you can find online.
Just remember that you want to take in less calories than you are burning if you want to shed some weight. It's also great to exercise when you get up in the morning & before you have had breakfast - the most important meal of the day. When you wake up, your body has basically been fasting all night and that is where the term "breakfast" comes from... because you are literally "breaking the fast" from overnight. So if you exercise rigorously in the morning, your body has no calories to burn off and so it starts burning fat immediately, whereas if you exercise heavily after a big meal, your body just ends up burning off alot of the calories you just digested. Whether you workout in the morning or not, always make sure you eat a good, healthy breakfast! This meal gives you your energy for the day, and it helps keep your metabolism sped up.