The best way to keep a pool clean is to keep it covered. If you do not have a cover a large tarp will do the job nicely as well.
Another easy thing to do is to either shower off or hose off prior to entering the pool this avoids getting hair and skin care products in the water.
Using an old pasta strainer for any small debris that accidently gets in the pool is another great idea
Using a 1/4 cup of borax to help keep wading pools clean also works nicely.
Add one cup of baking soda after washing, cover the pool for the night, and it will be bright and sparkling in the morning.