For a basic weight routine cover the 4 main exercises...
Bench Press
Squats
Deadlifts
Pullups
These 4 exercises, if done properly, will hit every major muscle in your body.
Then what I like to do is at least 2 isolation exercises for each of those 4 main exercises. So no less than 12 exercises all together. On bench press day I'll do the bench press (alternate between wide, medium and close grip), tricep pressdown (or skull crushers), incline bench, various shoulder exercises.
Squat day- squats, leg press, calf raise, weighted ab machine.
Deadlift day - DL's, stiff legged DL's, bent over barbell rows
Pull up day - pull ups, seated cable rows, shrugs and EZ bar curls.
So I perform isolation exercises that use the muscles that were used in my first compound exercise.
Stay in the 6-16 rep range, perform around 5 sets an exercise (no less than 3), always go to muscle failure, always use a weight you can handle, always have good form. Don't compare yourself to others at the gym.
^This post should probably be on top of every page.