If you want to hit it long and in control you need to spend time at the gym, although someone who is 140lbs can hit 280 (and I'd bet that is NOT his avg drive, have someone with a rangefinder mark his distance for a round and I'd wonder what that would compute too) if he wants to go farther he needs to build more muscle mass. Tiger probably spends time every day in the gym or on conditioning outside of swinging a golf club. He can drive well over 300 because of his physical conditioning not just swing mechanics.
Bottom line if you want to hit farther you need to condition yourself.
For a routine I'd say most people would benefit the most from a rigid core exercise from basic situps to planks and resistance training around your mid section. I like the advice of seeing a personal trainer locally, a good one will find and help address most of your issues a lot faster then you would be able to alone.