Block heaters are the best, if the hole is already in the block as FieroClint says thats good. Also a heater for the battery is very good, they wrap around the battery like a blanket and you plug it in as well as the block heater. The car may start but it is nice to have the oil flowing nicer around a warmer block.
Putting the heater on a timer is good as it saves money on the Hydro bill. Its a waste of electricity to put it on a warm block, six to eight hours before you need it would be good.

Always remember to unplug it when you leave home, you do not want your friends to see you are dragging the extension chord under your car.