Lift and eat. Bench press, shoulder flys/shoulder press, bicep curls, pushups, and pullups are some of the best upper body exercises. To capitalize on your lifting, you need to give your body the fuel it needs. Aim for 1 gram of protein per pound of bodyweight every day. Also aim for 2800-3000 calories per day. Meat, nuts, and dairy products are packed with protein and have tons of calories. If you don't eat more calories and you burn, you won't gain weight.
Also, don't forget to work your lower body, too. Nothing looks dumber in the gym than seeing a guy with huge arms and chicken legs.