Your pool filter should be kept very clean. You will need to clean it “as often needed”, which can be as much as once per week in areas with lots of deciduous trees (leaves fall into the pool), or can be a little as once per month for areas with little debris falling into the pool. It helps to keep your pool covered at night and even to set up an owl decoy to discourage songbirds from perching (and pooping) near your pool.
The best filters are cartridge filters, as they provide maximum flow while wasting little water to do so. They need to be cleaned as little as a few times per year. They might need extra cleaning after heavy storms and are, like all filters, dependant on the condition of your pool. These filters work best when cleaned every 4-6 months. You can easily remember to do this by doing it every time you get your oil changed on your car.
For extra cleaning, try soaking dirty filters in a 10% solution of muriatic acid or trisodium phosphate. Always handle these chemicals with care and use eye protection and hand protection. Rinse when finished and let it dry before putting them back in the pool.