Some suggestions for putting on muscle weight:
1) "Go to failure / no pain no gain:" If you want muscle growth, you only need to do one set, but you must do as many reps as you possible can. That means not being able to do one more rep, because you muscles are totally used up. That means you are probably grunting and vocalizing on the last rep or two (don't go to a gym where you can't vocalize.) The idea is to send your brain a message that the muscle you just exercised needs more of the bodies' resources to be able to handle a future load. If you do not go to failure, the message to the brain is that task was handled adequately and no additional resources are needed. (After doing a set of squats, you should initially have trouble walking, because you used up all of your energy. A fixed squat rack is very useful, because it allows you to "just let go" of the weight.)
2) To assist with step 1, get a partner to mutually help each other get motivated to go to failure. The partner also helps you avoid injury and/or dropping the weights.
3) After finishing your workout, drink a bottle of Ensure or a similar protein drink to stop your body from breaking down existing cells for energy. Do this quickly.
4) Don't eat junk food because eventually it will make you fat.