Identify what it is that you need more work on and search for materials on it. Ask your language partner if he or she can explain to you on it.
Understand the grammar and see how it's being used. When writing or talking with someone in an exchange, choose a particular topic that would give you practice in writing or speaking in the area that you need help on, whether it may be grammar or expressions.
Offer to go over grammar on the language that you can help the other person with and see if another day, the other person can do the same.
While going over the grammar, you can practice translating the phrases with the person, so it's a win win situation for both.
Good luck on your studies and your next tests!
You could also look for past papers and practice a little.
You should stop looking for a "magic bullet", Cathy. Try hard. Do you? If so, try harder. Language partners is a "band aid solution". Get some good teacher. There are loads of on this site.
Good luck with your English and never lose hope.