Good question, Make sure your gutters are the correct size in relation to your roof’s pitch. Make sure your gutters are not full of debris thereby eliminating splashover. Do not leave area rugs on deck for an extended period of time (deck will remain wet) Make sure you clean debris (pine needles, etc) from between boards. Clean twice a year (once after pollen season, once after leaves have fallen). You can DIY this. Blow leaves off decking in fall (do it daily). Following these guidelines you’ll minimize long term mold, mildew growth.