Pulling the boards into place is not easy--so often we drive a chisel into the subfloor and use it to ratchet the boards tight for nailing. It always works better with 2 workmen.
Thresholds and in particular nosed thresholds at the top of stairs should look like the existing stair treads. You can rip a piece, glue, nail and screw to emulate the same look in most cases. Hide your screws where you can.
Casings and jamb extensions will often need trimming so that the flooring slips under and doesn't leave an unsightly gap. We use a flush cut backsaw (a saw that cuts on the pull stroke--Japanese steel preferred), and rest it on a piece of the actual flooring for a guide.