Among the most effective things is to swing a weighted club. You work those golf specific muscles that way. Not full-speed swings, but quarter-speed, half-speed, etc. Doing an exercise regimen designed to increase flexibility is another option.

Having a pro look at your swing for power leaks, as tt suggested, is also an option. Perhaps having a complete fitting done finding the perfect driver head and shaft could be looked into, also. With that speed, you probably should be hitting at least an 11 degree driver, maybe higher -- depending on your angle of attack.