The best way to increase muscle size is pushups and lots of them. Free weight training yields disproportionate results compared to pushups.
As for the question...
To increase muscle size....
By a lot of free weights I hope you mean > or = 20 lbs
lift a lot of free weights and DO NOT stretch vs.
* Find yourself in the doctors office sometime soon.
--> muscle growth goes a lot slower, as you spend more time resting injuries rather than training
lifting a lot of free weights and DO stretch
* Find yourself keeping at the workout
--> muscle growth goes faster, as you spend more time training and little time resting injuries