Getting Stronger But Not Heavier

I’m training for the next volleyball season which starts in september. During this time i want to get quite a bit stronger and more powerful than i am now, but not necessarily much heavier so i can maintian my mobility and increase my vertical.

Any suggestions or tips?

my current stats:
6’1"
185 lbs
squat: 280
DL:315
Bench:185
30 inch standing vertical

Search function.

http://www.T-Nation.com/free_online_forum/sports_body_training_performance_bodybuilding_strength/gaining_strength_without_gaining_weight

thanks bud