How do I reduce the number of screw pops in my drywall?
Where I'm from, the ceiling schedule for drywall nails and screws is 7" O.C.  From your description you're closer to 11" O.C.  Particularly when you're using a heavy sheet like a 12' x 4' x 5/8" sheet I recommend strongly a jack to hold the drywall in place as you screw it.  You can rent one at any major tool rental yard.

Also may I recommend picking up a carpentry or plasterer's textbook.  They offer many helpful tips and techniques for a stellar sheetrock job.  Two examples:  "Carpentry, 5th edition" by Leonard Koel, or specifically for drywall: Gypsum Construction Handbook, Centennial Edition 2000, published by USG.