Always watch your dog when they are in the pool area. Don't leave them unsupervised.
Fence off the pool to prevent unsupervised access. Self-locking gates are best.
Install recessed steps so dogs can exit easily. Ramps are another good option.
Have your dog wear a flotation device for safety and visibility.
When not in use, remove ladders your dog could use to climb into the pool.
Properly balanced water is less irritating. Test pH, chlorine, etc. regularly.
Consider alarms that detect vibrations or waves to alert you if your dog falls in.