There are varying schools of thought, each with a certain amount of science to back them up. Personally i do 8-10 reps of 40% of the set weight, followed by 2 reps at 70% (the heavy set to get the muscles accustomed), followed by a 6 rep set. If you do too much of a "warm up", you may lose the intensity of the work out, and simply create muscle endurance. Both intensity and endurance can build muscle, however, low rep, heavy weight intense training, with the correct amount of rest days will lead to the greatest muscle development. The dudes who go to the gym every day and lift the same weights are not giving any time for their muscles to recuperate and for the muscle fibres that have been broken down to repair. Size growth will still occur due to the endurance factor, but no where near on the same level.
Also make sure u have a balanced, but high protein diet for maximum results.
peace