If you will be working with 485's first, I would recommend starting with any resource material in the office. Also there are stickies at the bottom of this forum with recommended reading. Then you can always do an internet search on hh, and look for books by Tina Marrelli, good references for hh.
I suppose it depends on what you mean by "doing 485s." In addition to the stickies, also check out the home health section of the cms.gov website and your state's home care association for state-specific rules. Tina Marrelli's manual for home health documentation is also one of the best pocket resources for everything related to documentation and has been updated for OASIS-C.