A sharp mower blade is a key to a perfect cutting job. However, whenever you sharpen a blade yourself, always check it for balance. An out-of-balance blade can cause excess mower vibration and wear. One way to check is to tie a metal washer onto a string, thread the string through the center hole of the blade, then hold the blade up with the washer supporting it. The washer should be on center and turned perpendicular to the blade. The blade should stay level. If it doesn't, grind it for balance on the back side of the blade. Always disconnect the lawnmower's sparkplug wire before removing or replacing any blade.
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.