Skimming the leaves and debris off of the surface of the water is a no-brainer, but it bears repeating. For a truly pristine pool, skimming should be done daily.
If you have a bit of money to spend, consider buying a robot vacuum that will clean the bottom of the pool for you.
In addition to skimming, you need to scrub the sides of the pool to prevent algae build-up. Thankfully, that doesn’t need to be done quite as often. You can get away with scrubbing once every other week. Just look for any growths and go at them with a scrub brush to keep your siding looking fresh and clean.
For those particularly stubborn spots that won’t go away with any amount of elbow grease? Repurpose an old sock. Fill it with chlorine and let it sit on top of the spot for a few hours before scrubbing once more. The chlorine will eat away at the algae and you’ll finally have a use for those socks without pairs. It’s a win-win.