word choice - think, I think, I don't think

I use "think", "I think" and "I don't think" in my writing a lot. Can you suggest a few ways to reduce it and few alternative ways of saying the same thing?

Look at the below sentences I have written. These are just few examples, I use them a lot. Average two or three "think" in one page.

1. Why do you think about that?


2. I think you can do it.


3. But I think you got to take some rest.


4. Do you think you can break that?


5. I don't think so.