Given that it is a College English Test, I would suggest reviewing a lot of grammar. The best way I find is by helping others in their grammar. Sometimes, the best way to learn is to teach.
I'm assuming you have an advanced knowledge of English grammar at this point. What you are basically doing is reviewing. The best way to make the review stick is to give it purpose. When someone depends upon you understanding the material, you will find that the information you review and teach will stay with you longer.
If there is an oral component, I would start scheduling some audio or video chat sessions with some native speakers here.
I hope this helps. Good luck.