The next reason a ball is topped is because you set up with your arms extended, and by the time you hit the ball, you do so with your arms bent.  This bending of your arms (aka: chicken wing) shortens the swing arc versus the one you started with and again the club comes into the ball higher than when you started.

So how do you stop topping the ball?  Answer: Swing easier!!!  Think about it for a second.  If you are a beginner, wouldn't you rather get the airborne than hitting it along the ground.  Obviously you said, yes!  If you get every ball in the air, you are hitting shots with more consistency than if you roll them along the ground.  Once airborne, you will gain confidence.   Then, you can start to work on distance and accuracy.  So for beginners, this should be priority one.  Your thought shouldn't be, "I'm going to crush this one".  Your new thought should be, "I'm just going to get this ball in the air".  Trying to crush the ball is like running before you can walk.  Why would you think that you can do something that it took a better player years to master?  

For the average player that tops the ball, you have to slow down a little and allow your arms to relax throughout your swing.  Again, those topped shots are coming from you trying to hit the ball too hard.  Your thought should be that you are never going to swing over 80% of your ability.  You are no longer going to try to impress your friends, keep it up to the long ball hitter in your group, reach unreachable par 5's in 2 shots or take less club and try to overpower the shot.  For you, slowing down and swinging easier will eliminate these topped shots.  Once you eliminate the topped shots from your game, you will reduce your score giving you more confidence that will take you game to the next level.

Slicing

This shot not only has your swing path to the left but it also has you with your clubface open at impact.  This means you actually have 2 flaws when you hit a slice.  Now, if you are someone who hit this type of shot, you have to get the clubface squaring first.  Think of a pro for a second.  When a pro hits a ball, the clubface is not coming through wide open, it is relatively square.  So the next time you go to the range, do some practice swings rolling the clubface closed through impact.  Then,  keep rolling your wrists over earlier in the downswing until the ball hooks to the left consistently.  I know that hooking the ball is still a bad shot but If you can consistently hook the ball ... you are no longer a slicer!

Once you get it hooking consistently, it's time to work on the direction of your shots.  So forget rolling your wrists and focus on turning your body to start the downswing.  As you turn properly in the downswing, you body will tilt to the right through impact.  If your body tilts right, your club will swing out at the ball thus changing your swing path.  If you couple this outward path with a squaring face, you will not hit the ball straight or with a slight draw.  Now the slice is gone forever!