A few points I'd like to make.
1) Keep a log of food intake. How many calories are you getting each day and how are they divided into proteins, carbs, fats? Also log your body weight. If you stop growing, add food.
2) Eat prior to your workout (as close to workout time as your stomach can deal with, I can even eat during heavy weight sessions) and eat immediately after each workout.
3) Keep a log of your workouts. Just starting out, you should see big gains in strength, and possibly size very quickly. Then it gets harder. Don't get discouraged when you start hitting that first plateau.
4) Lift heavy, and watch your workout logs for stagnation. You'll want to change up your routines frequently to keep your body adapting and growing. So, for example do 5 sets of 5 reps on your heavy lifts for 2 weeks or when you start to have trouble increasing weight. Then switch to 10 sets of 3 reps. Keep it changing, keep it interesting, and you'll keep growing.
5) Learn how to properly do back squats, front squats, and deadlifts. They are all essential lifts if you really want to grow. Focusing on biceps and pecs won't help you. I personally enjoy the olympic lifts, and recommend them highly, however, they are difficult to learn without some coaching. Work your whole body, but concentrate on the largest muscles.
6) Have fun.
