Distance and handicap have nothing to do with each other. My dad routinely out drives his good friend by at least 30-40 yards, there handicaps are nearly identical. I've played against single handicap players who i out drive by 40-50 yards.
There are a few things, but i think what seperates the long drivers from the short drivers are a few things,
overall height, 4 out of the top 5 in driving distance last year were above 6'3, that's not saying a short person can't hit the long ball, look at the long drive champion Sadlowski, and Rory, there both less than 5'10" and bomb the ball, but they do some key things.
1) they get amazing seperation between there hips and there shoudlers
2) they have really good mobility in all there joints, especially shoulders and wrist
3) they have incredible hip rotation speed, rory being one of the fastest hip rotations on tour
Some people claim the X-factor is the key to distance, its important, the hips drive the power. the rest of the body just transfer's that energy to the ball. You can create a higher x-factor by having your hips fire first while your shoulders are still rotating back, or stopped rotating. This is why getting the correct start of the downswing is important. A lot of people start there downswing with there hands, this is a huge power loss.
If you want to increase distance,
1) workout, build up mobility and strength around your joints (especially hips, shoulders, wrists). Focus on getting powerful strength in your lower body (hamstrings, quads, gluts). TPI has some great material on mobility and strength. But if you want some information on Gluts, youtube Bret Contreras, he has done tone of research on glut activation. Key areas for those of use who have been sitting in seats or on the couch most of our lives, any muscle around the hips, especially hip flexors, which help bring the knees toward the chest, these muscles will help you keep in your swing posture better. I started adding P90x abb ripper program to my workouts. After my first time through, my abs were fine, my hip flexors were gone, i couldn't stand up straight for 4-5 days, i looked like an old man walking. Now, i have no problem with my hip flexors.
2) work on sequencing your swing correctly, there was a thread on which we talked about the kinetic chain, if you look at Rory's, his hips rotate at about 700 degrees per second, his clubhead is moving 3x that amount at impact.
3) hit more up on the ball, this will decrease your backspin
4) make better contact, get some impact tape or packing tape + magic marker works good to, get that ball to hit just above center of the clubface