The funny thing about a lot of people in the gym is that they really want results and work relatively hard, but they stay away from the exercises that will actually give them the best results. For example, if you are spending 30% of your time at the gym working on your arms than you have a serious problem. You want big arms and nobody is blaming you, but for most people the key is staying focused on the basic compound lifts. Compound lifts need to be your bread and butter if you really want gain serious mass and strength.
The following exercises are the most powerful tools for any fitness enthusiast to have in their arsenal
Bench Press(Flat,Incline,Decline)
Squats(Back and Front)
Dead Lifts
Lunges
Barbell Row
Pull ups(all grips)
Dips(For you savages out there Hang a couple 45lb plates from your nuts and get down)
Military Press
Upright RowNow I'm not saying these are the only exercises you should do but at least 80% of your time in the gym should be spent hitting every single exercise listed without neglect. This means that you can't cling to the bench press because it's your favorite exercise, you better be giving that squat rack just as much love.
Try keeping your training routine well rounded so you don't have any weak points. A routine that gives equal attention to all muscle groups will help your body develop to it's true potential. Do you want to be one of those guys walking around with a huge upper-body and little pencils legs? These guy gets made fun of more than anyone, so trust me you don't want this to be you. The moral of this story is to really stick to all of the compound lifts and never neglect your weakest exercises. Never favor the bench press over the squat rack or you might turn yourself into a human S.U.V. and they don't call them super useless vehicles for nothing.
