Make it enjoyable. Find something that you like or is fun to do. The no pain, no gain philosophy has now been replaced with proper technique, range of motion, warm-up, stretching, injury prevention, and rest and recovery. Do a variety of exercises or sports. Doing the same exercises over and over can be boring.
Variety is the spice of life and the key to long term exercise habits.
Warmup, Cooldown and Stretching. Rest and Recovery. Get plenty of rest. A good nights sleep is as important as the workout. When you are sleeping is when the body does all its repair and rebuilding.