Flexibility should be the topmost priority of a golfer. Next comes stability. Without these two attributes, other fitness aspects won’t be that effective.
The flexibility of joints will dictate the range of motion and without a proper range of motion in the hips, shoulders and thoracic spine, it is not possible to generate a good golf swing. You cannot fire a cannon from a canoe. A stable lower body gives balance and strength for power generation.
A lot of people don’t realise the importance of the legs and hips in the golf swing. They over emphasise on shoulder turn, etc. Get strong legs. The great Jack Nicklaus once remarked that his hands were so weak, he would sometimes ask his wife Barbara to open the jam bottle for him. But, he had legs like tree trunks. All power in moving and rotating mechanics start from the ground and the legs are the first point of motion in a body. Squats, lunges and deadlifts are the best way to develop strength in the legs.
Golf is rotation: Understand the mechanics of rotation, particularly rotation in the thoracic spine. Most people have tight upper spines because they are locked all day in rounded postures. Not surprisingly that we cannot rotate the thoracic spine - what cannot extend cannot rotate: - It’s simple biomechanics. So, they compensate by rotating from the lumbar spine and this leads to poor ball contact, spin-offs and weak slices. Also, it is the primary cause of low back pain in golfers.
Many players warm up before a round of Golf but don’t cool down or stretch after the round. Not stretching after the round makes muscles chronically short and tight. Remember to find a quiet corner in the changing room or golf range to stretch out after a round. This will prevent a lot of injuries.
Get a strong mind. Remember in golf don’t expect; Learn instead to accept. You can improve your mental strength by not getting seduced by results, ignoring unsolicited Golf advice, stop sulking and believing that you can do it.