The butt end of your club should be pointing roughly to your sternum throughout the swing. In other words, keep your arms swinging in front of your body, not around it. This promotes a swing away from and back through to the target.
Topping the ball is caused by trying to lift the ball up in the air and keeping your weight on your rear foot. Think of swinging the "Y" formed by your arms and shoulder through to the target and allow your weight to move toward the target.
When playing in wet conditions remember to choke-up a little on the club instead of gripping the club at the end of the handle. This will give you better control and make it less likely to hit the ball fat due to the soft turf.