first ... good form ... clean steps, solid hip turn, and good acceleration / follow through ...
when I get some OAT issues, the first issue is usually related to my lead shoulder (I throw RHBH, so this would be my right shoulder). When it "flies open", I pull my drives high and right. I then try to focus on keeping it "closed" all the way from reach back to follow through.
I also find OAT happening when I accelerate too quickly, and get my hips back to the target too early.
Another issue is related to my reach back. I shorten my reach back for slower discs. A putter or mid-range doesn't require as much arm speed to get up to cruising speed. I tend to strong-arm putters with reach backs that are too long, which dissipates my "snap".
Last issue I could think of, is how you "telegraph" your disc during the reach back, and then "transfer" that arm angle into the throw and follow-through. Any minor change to that initial angle will impart some OAT. And if the discs you were throwing are susceptible to "squirrellism"
then that OAT will be magnified.