Improving strength and power is not only important for golf, but for health and everyday life too. HERE is a playlist on Youtube with 50 videos of strength and power exercises to help golfers.
A couple of things to remember when looking to improve strength and power.
Power is about intent... you must try to move as quickly as possible (even if using relatively heavy load and it doesn't look quick or fast, with intent, you will improve power.
Beginners can improve strength without high loads, but more advanced lifters will require 85% 1-rep max to see improvements in strength (thats about 6 reps or less).
As with all training, you must use progressive overload. This doesn't mean increasing load/weight every session or week, but gradually over time, you will have to.
You can progress strength training by increasing reps, sets, range of motion etc, however, for maximum strength, increasing the load is important and increasing other variables like mentioned above can sometimes negatively effect max strength.