There are some jobs—and some screws—for which I always use a hand screwdriver, never a power drill/driver. Those jobs include hanging cabinet hardware, installing doorknobs, and tightening the screws on switches and switch plates; basically, any task where the bit could easily slip and permanently mar a surface. Soft brass and aluminum screws also fare better when turned by hand, as do slotted screws of any kind. A slotted bit in a drill is virtually guaranteed to slip off. But when it's a Phillips or square-drive screw and it's long enough to require a pilot hole, I'll go ahead and drive it with a power tool.
Phillips-head screws, unlike slotted screws, can be turned with a screwdriver held at a slight angle. Ideally, I always try to hold the screwdriver in line with the screw's shaft. It's the best way to avoid stripping the head.
Wrench It Free
If I need extra torque to loosen a stubborn screw, I'll tighten an adjustable wrench on a square or hex-shaped screwdriver shaft. With its movable jaw positioned on the side I'm turning the handle toward, the wrench provides a second handle to persuade the screw to move. If it's really stuck, try tightening it a quarter turn to break the seal.
Matching the Tip to the Screw
Nothing ruins a screw faster than a screwdriver tip or bit that's too small for the slot. If there's any play at all, the tip's hardened edges are likely to tear up the screwhead. My general rule is to start big and work down until the tip fits snugly in the screw's recess. With slotted screwdrivers, tip width is also critical. A tip that's wider than the screwhead will end up scarring the surface as you make the final few twists. It's not that difficult to have the right tip on hand. All I ever need in my work are three sizes of slotted screwdrivers, three sizes of Phillips, and a couple of square drives.
Tip: When you're shopping for a screwdriver, pick it up and give the handle a good, hard squeeze to make sure it's comfortable. If the handle digs into your palm, better keep looking. My favorite handles have a triangular shape in cross section, with rounded corners.