I'm posting this because these two exercises are supposed to reduce lower back injuries, which is something most golfers need. This Golf Digest video from Ron Kaspriske is also supposed to help you create more power with your swing.
The video is pretty much self-explanatory -- it teaches you to do some lateral squats and twists, combined with some diagonal stretches.
I'll add only one thing to this, and it concerns the weights. You don't need heavy dumbbells or medicine balls. That huge fantasy novel you've been planning to read will suffice, as will a small sack of potatoes or a container of antifreeze (or any liquid, for that matter) up to a gallon. Judging by the size of the weights in the video, ten pounds is plenty for these exercises. (A gallon of water weighs just over 8 pounds.)
Again, let me stress that these two exercises are supposed to help reduce lower back injuries, which means lighter weights are better than larger ones -- especially when you make that diagonal reach. I repeat: Don't overestimate how demanding that move will be, even with smaller weights. If you try this, start with lighter weights, rather than heavier ones.