Most golfers don't take enough club when playing par 3's.  What you should do is figure the yardage to the back of the green and select a club that will reach that point.  A less-than-perfect shot will still get you on the green.

When facing an approach shot from the rough, move the ball back in your stance to help you hit down on the ball.  Also open the clubface a bit to offset the club's tendency to close as it goes through the grass.

When facing a tight lie, a lot of wind, or a very firm green on a wedge shot, it may be more advisable to hit a knock-down 6-iron than a wedge.  The key is to keep your hands ahead of the clubhead through the impact area.

When a hole dictates that you should hit a soft draw for an approach shot, position the ball just back of center in the stance, close the clubface a little, try to stay behind the ball, and release your hands through impact, letting the club do the work.

Hitting your driver off the fairway often helps on long par4's with an open green.  Remember to choke down on the club about an inch-and-a-half and move the ball back in your stance.  Swing a little shorter and easier.