How do I win competitive grants that keep getting rejected?

You can write a solid grant, which already puts you ahead of many. The competitive ones defeat you because there the bar is not competence, it is standing out among many others who are also competent. That is a different game, and losing it does not mean your writing is weak. In a crowded field, the winning proposal is usually the one that most clearly answers what the funder actually cares about, not the one that is most polished. Study past winners. Learn what that funder rewards. Make your case sharp on the one or two points that matter most to them, and cut everything that does not serve those points. And accept that even strong proposals lose often; the ones who win are usually the ones who kept applying and kept refining. Before your next submission, find one funded proposal like yours and study what made it land. You are not failing when a competitive grant says no. You are gathering the information that turns a good writer into one who wins.