If entering the US Army as an E4 Specialist, how long to make Corporal?

I'll be going to OSUT at Ft. Benning in January. I'll be an E4 Specialist. I'll be in infantry with an Option 40 Ranger try-out. I really want to become an NCO as fast as possible, so I'm very interested in the lateral promotion to Corporal. I realize that it is a merit-based and leadership-based promotion in most cases. I also understand that my chances might be better serving in the combat arms, which is a plus. I just want to know from some current NCOs or officers what the best ways would be to go about snagging that lateral promotion. Any constructive input helps.