The depth of your cabinetry is key in determining the proper screw length. The screw should be about 1/4" longer than the depth of the door or drawer. If you use a screw that is too long you'll risk damaging the knob or pull by pulling out the metal brass insert.
We provide 1 1/4" length screws with all knobs and 1" length with all pulls. However door and drawer thickness will vary and you may have to visit a hardware store to meet the specific need of your project.
It's always best to hold the handle flush against the drawer or door when screwing in the screw. Screw one end partially and then do the same with the other end. Then tighten screws. You don't need an electric screw driver. The most important thing is to keep the handle against the drawer (no air between the two) the entire time you're using the screwdriver.