Depending on your grip choice. If you have an eastern(ish) grip, you have a fairly easy time blocking back serves if it's within your reach. Use the serve's pace and focus on making good contact with the ball off the bounce, take it early, and block it back with good placement (if you can).
Lastly, you don't want to slice ALL the time so that your opponent knows it's your go-to (or perhaps the only shot).
If you have a western(ish) grip, I'll have other people help you. But still, your focus should be take it early, use the pace of the serve, and block it back deep/good placement.
I know this wasn't your question originally, but if you're a junior, there's no reason why at 5'6, you're ~160lbs. I'm not picking on you, but it'll be tremendous for your game if you can drop at least 10 pounds.