A way to get a good fit when installing decorative molding is to install the first piece with a square end. Then cut the second piece at a 45-degree angle in a miter box or saw to expose the profile. Use a coping saw and follow the edge of the profile, under-cutting it about 3 degrees. This lets you get a good fit, even if the corner is not perfectly square.
A piece of pipe insulation wrapped around a screwdriver handle will give you a better grip when you need more torque, or when the handle is just plain slippery.