Most of the people on OKC that are a high match% for me are poly or ok with open relationships because I've made it a high priority in my questions answered. I've been lucky to have a strong poly community locally where I can meet people, but I've also met a few through OKC.
When I message people I comment in a way that makes it clear I've actually read their profile. My wife puts in her profile that she'll respond to anyone that sends her a link to a webcomic, and very few do. Also, for photos, I make a point of using ones in which I'm doing something I enjoy, not just standing and smiling for the camera. It seems to help.
When I was more actively using OKC (too busy trying to see the people I'm already dating now), I found I could message people for a couple months and rarely hear anything back, then get messages from several people and have dates with 3 different people set up. It doesn't always make sense, just work on your profile, answer questions, post good photos, and message at least a couple people per day that genuinely interest you.
Outside of that, you may actually get better results simply going out and doing what you enjoy and seeing who you meet along the way, maybe trying meetup.com. Also, see if you can find any local poly meetup groups.