Assuming your opponents are even slightly aware, c/r'ing every once in a while will keep them honest.

If you feel you are getting predictable, use simple game theory when you are torn. E.g, whenever you whif and don't have a good read, check your clock for odd/even minute. Bet on one, check on the other, which keeps you random against thinking opponents.

My c-bet decision is more related to the number of preflop callers than a set % when I miss. But, I do check sometimes when I miss.