What could be causing the car to shake after a tune up was done on a 2002 Pontiac Grand Prix SE?

were the plug wires replaced in the right order or did they get mixed up? were the new plugs properly gapped before being installed? if you didn't use new plug wires, maybe a broken plug wire? make sure the plug wires snapped onto the head of the plug securley what all was changed out when you had the tune up done?