Develop a program. Decide which exercises you'll do on which days. Some exercises focus on a specific muscle (e.g. bicep curl) while other exercises call upon several muscles at once (e.g. squat). The important thing is to make sure each muscle gets a chance to rest for at least a full day before using it again. For example, you can do a full-body weight training routine every other day (with cardio in between, if you want) or you can alternate muscle groups (arms on Monday, legs on Tuesday, upper back and chest on Wednesday, etc.).
Muscles grow during rest, not during training. If you don't give a muscle adequate time to recover, you'll actually interfere with the muscle building process. When you lift weight, you're supposed to stress the muscle to the extent that it breaks down at the cellular level, resulting in increased protein synthesis, which produces thicker muscle fibers. This process begins 2-4 hours after the workout and lasts 24 hours (although some researchers suggest that muscles worked to exhaustion need 36-48 hours to rebuild). If you stress the muscle again before the process is complete, you'll break down the muscle fibers before they've had a chance to rebuild.
To build volume rather than strength, design your program around lots of repetitions (10 to 12), three to five sets, and short (30- to 90-second) rest periods between sets. Athletes looking for power and strength, on the other hand, will favor a program with reps that max out at around six and sets ranging from two to six, with a long rest period (two to five minutes) to promote better recovery between sets.
Change your eating habits. You can't build muscle unless you give your body the proper building blocks to do so (and stop giving it junk). There are also plenty of supplements which can give you energy and aid in muscle recovery and repair, but remember, they are supplements, which means they only work in conjunction with a good, consistently followed exercise regimen and a proper diet.
Incorporate complex carbs and protein into your diet. Focus on lean protein like egg whites and low fat yogurt, and whole grain carbs like oatmeal and whole-wheat toast. Avoid sugary, white processed foods; they interfere with your glucose levels and immune system.
Eat small meals throughout the day. This gives your body a steady supply of fuel to build muscle. Eating in "spurts" (2-3 large meals per day) should be avoided because it hinders muscle growth during the stretches between meals. You should eat 5 to 6 small meals a day.
Since creatine provides energy, take this supplement about 45 minutes before a workout. Look for products that pair creatine with carbs, as this combination increases the rate at which the creatine is absorbed by your muscles. Consuming creatine with a glass of juice will have the same effect.
Drink sports drinks during your workout. Look for drinks that contain carbs and protein. This combination reduces muscle damage and hastens recovery.
Get a carb-loaded drink or snack (1.5g of carbs for each 2.2 lbs that you weigh) within 30 minutes of your workout to stimulate an enzyme that helps the body produce glycogen.
Have a whey protein drink within 30 minutes of your workout to help your body repair and rebuild lean muscle tissue.