One of the easiest ways to keep up with modern trends is to make a rental property as simple as possible. Paint it white or a light beige, have minimal furniture at the showing (or none, depending on what was in your advert), and make the area as bright as possible. The use of mirrors, especially across from windows will make rooms seem brighter and larger. White walls, although not always desirable by the client, will ensure that a room doesn't seem dark, small, or dated as colors go in and out of style almost daily.
Furniture is a trickier beast to tackle, but thrift shops can be a landlord's best friend. While yes, many things you find will be dated as well, there are a few gems which either are new and discarded or help to cause the old phrase to ring true once more. Other things such as rummage sales at different buildings, churches, or yard sales are bargains just waiting for you as well. Also, Charlotte NC has a few different colleges nearby, and you would be surprised what some students give or throw away. Near the end of the year, take a drive by and see if you can help any students by taking something bulky off their hands. If you have flea markets nearby which only happen on weekends or such, wait until the last day as people are packing up to make an offer as well. Many vendors will be more willing to cut a better deal at this time, as they don't want to have to take their items away just to bring them back in a few days.
As for keeping up with the ever-changing styles of homes and buildings, do yourself a favor and either take a couple of hours a week online to check up or glance through design magazines while in line for your groceries. Better Homes and Gardens, although older, is still a leader in design and you can copy many of their images with cheaper items than they use. Keep an ear and eye out, and remember, some classic styles never do really go out.