What is the best way to repair bad credit in preparation for getting a home loan in 1-2 years?

I have a few charge offs from 3-4 years ago, and 2 that went into collections which I am making payments on. I now have a car loan that I always pay on time which is improving my credit score. Is there anything that will improve my score and chance of getting a home loan other than getting a secured credit card and keeping it paid on time? Do the charge offs have to be cleared from credit before getting a mortgage is possible? I will have a down payment when we do apply, but wasn't sure if the negatives have to be cleared, or if I just need to show improvement over the next year or two. Thank you for any information!

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