Screw drivers are pretty simple tools. That said, here are some tips on using them.

• A Phillips screw driver can easily "cam out" of the head of a screw unless it fits that screw perfectly. Avoid cam out by using the right size driver for the screw head. Pick guard screws require a #2 Phillips screwdriver head. Trying to use a #1 driver increases the likelihood of cam out and potential marring of a finished surface.
• Screw drivers aren't chisels
• Screw drivers are aren't pry bars
• Using two hands is important: one hand to drive the screw, the other hand to guide the head of the tool. Using two hands may seem tedious, but it's well worth the effort. All it takes is a single "cam out" and you'll put a dent or scratch in a finished surface. I've done this too many times.
• Flat bladed screw drivers, in my estimation, have no place in guitar building. However, you may encounter the need for a small blade to loosen set screws in some control knobs.
• There are two sizes of Phillips head screws used in guitar building--the #1 and #2.
• A jewelers set of screwdrivers is good to have in case you encounter those tiny screw heads at some point
• A long #2 Phillips screwdriver, 8 inches or longer, is good to have to adjust saddles from the rear without interference from the guitar's butt.
• Powered screwdrivers are super cool to use, but do require a higher level of care. They make it very easy to destroy your work if not super careful.