Practice is a great key as was stated above. also check out this video, http://thesandtrap.com/t/39411/quickie-pitching-video.
I also think it helps if you focus on your target and use a repeatable routine. When chipping or pitching, I look at where I want the ball to land, whether it is a chip and run, pitch or flop. I keep staring at it when I address the ball. Then I aim the club face to the target, look back at the target, then head down and execute. No time to think about technique or second guess, which may contribute to yips. If I do any practice swings, it would be just to check the rough for feel, but I don't do that when I address the ball.
A fun drill to do is play one ball at a practice green. Toss a ball into the rough. Go through your routine and pick a landing spot. Chip/pitch/flop to that spot. Then toss the ball to a different spot or putt to a hole. Toss the ball into different lies and try to get as close to the target landing area as possible, but with only one ball.
Best of luck.