Two suggestions:
1) While in the water adjust you leash at your ankle so that it points out, it will keep from tangling, just make a habit of doing that.
2) Try a thinner leash, the thicker ones float more and get in the way, plus they rebound the board at you less when they are thin
Also, remember that if you go for a smaller size it will leave less distance between you and the board, so more of a chance of your board hitting you.