Mistakes: Using a manual nailer Nailing into the groove instead of the tongue Using staples instead of nails
Other suggestions. Put down a long, dead straight board that will serve as your first course. IME, this is better than starting off with the actual flooring material since you can nail this sacrificial course straight down into the subfloor instead of using the angled nailer, thereby (mostly) assuring it won't move during the nailing process. Don't remove this board until you have butted at least 4 full courses against it, at which point the courses shouldn't move, no matter how much banging (manual or pneumatic) you're doing.
Make very accurate measurements wall to wall in various parts of the room to determine where to put this backer board. Be sure you're not going to end up with a 1/4" last course up against a wall. Opinions may differ, but I put my backer board in the middle of the room, then used a tight groove-to-groove spline so I'd always be nailing into the tongues (sp?) as I changed direction and started working toward the opposite wall.
Just one amatuer's opinion based on a job that turned out *very* well.
Joe C.