Greetings, fellow cuber. I speak to you from the other side. I am actually sub-20 (except when I'm not, and hopefully these pieces of advice might help. Don't look at the pair you are currently solving. Instead, while you are currently solving your pair, look around the cube for other pieces you can solve, so that when you are done with your pair, you can immediately switch to that pair. Then start from step one again. If you haven't practiced look-ahead, looking at your current pair will be a very hard habit to break. Trust me, I still have this habit sometimes. However, breaking this habit will pay off. I was able to shave off a 4 whole seconds off my times.
Additionally, I would suggest drilling cross as well. If you spend 5 seconds of cross, you can shave off an extra 4 seconds off all your times just by practicing cross. Here are some practices that might help:
1. Plan out the cross, then execute your solution. If you haven't practiced this much, you will mess up a lot. That's perfectly fine, eventually you will be able to get the cross perfectly without any mistakes.
2. After that, try to execute your cross solutions as fast as you can. Once again, this might be difficult, but after this, you've basically mastered the cross.
Hope this helps.