I dont do any exercises, but I always play in a comfortable position and stop playing if my hand hurts or whatever. And about the shower thing, Ive been playing for 3 years and showers still rip my fingertips apart, but thats cos I go for runs every morning then shower so never really have a chance to build them up. Izzy Stradlin from GnR used to go weeks without showering to keep his fingers hard, my girlfriends making sure I dont go down that road!