Everyone I have talked to says that claiming a small home-office isn't worth the increased audit risk, but I don't know if that's just urban myth or reality. At any rate, you should at least read
http://www.irs.gov/publications/p587/index.html and maybe some general books on landlording that deal with tax implications, or some books that deal specifically with tax implications of home businesses.
Regardless of whether you have a home office, you can deduct a percentage of office equipment- printers, computers, etc if you use them for business use, but only the percent that they are used for business purposes. Sometimes calculating out depreciation, tracking everything, etc is more hassle than its worth if your business usage is only a small fraction of total usage. You can also keep supplies separate - paper, etc, that are exclusively for business use and deduct those. If you have 2 or 3 rentals, though, trying to deduct things like a personal cell phone gets to be a big stretch - you'll maybe use it 1-2% for business, >95% non-business, unless your tenants are really high maintenance.