Do you have any routine procedures you do while at/pre/post gym?
I always sit with the weights on my lap, and stare at them in the mirror, counting in my head the amount of reps I'm about to do. Wierd I know, but it really gets me pumped to do the set. It actually works.
I also can't workout without my headphones, can't get into the zone without them.
I also always do a pre-workout poo (Call it my PWP) before every session, don't know how, but I always need one!