i guess you should be doing some of the following:
Bench press for your chest : maybe 4 sets of 8,7,6,5
Narrow grip bench press for the triceps: 4 sets of 8
Standing Barbell Rows. great for shoulders imo (lateral deltoids) i do 4 sets of 8
Lateral raises. another one for the shoulders. 4 sets of 8
Raises. again for the shoulders.
Shoulder press: for the front of your shoulders (anterior deltoids). maybe 3 sets of 8.
Bent over barbell rows: for your back. 4 sets of 8
Barbell Curls: great for building up your biceps. maybe 3 sets of 8
Concentration Curls: another good exercise for your biceps. 3 sets of 8
Barbell Shrugs for the muscles either side of your neck.
Squats and leg extensions for your legs
Bicycle Crunches are excellent for your stomach muscles. I do leg raises as well. Sit ups aren't worth a fuck imo.
Those are the exercises i normally do at the moment. I might do skull crushers (triceps) , dead lifts, pull ups and chin ups every now and again as well. I usually work out three nights a week and do between 5 and 7 exercises each night.
It is important that you lift with a weight that is a challenge for you but is not so heavy that you are killing yourself trying to lift it. It isnt a contest so who gives a fuck what weight the other guy can lift. Correct form is the most important thing. You need to make sure you are doing the exercises correctly. for example, while doing a bench press the bar should be lowered to touch your chest or little above it. I have seen guys lifting heavy weight on the bench press but are only lowering the barbell halfway. Lift with a weight that allows you to the exercise correctly.
Here is a good website that shows you how to do them:
ExRx (Exercise Prescription) on the Net
Diet is also important. You would need to eat about 1 and a half times your body weight (in lbs) of protein each day after working out. You could get a protein shake to help you do that.
Foods that contain alot of protein include:
Chicken
Tuna
Eggs
Milk
Nuts
Steak