Stuck on finding the most searched keywords

start with what the site already shows up for, search console, queries, sorted by impressions, because those are proven. then google keyword planner for the volumes and ideas (free with an ads account, no spend needed), then type the main phrases into google and write down the autocomplete and people-also-ask questions. the thing to resist is going for the most searched phrase. the one with the biggest number is usually the one a small site can't rank for and the one that converts worst. medium volume, clear intent, that's the list.