How can I learn to see trends in rental property markets

[Andrew Rodriguez]

Hello all! 

I'm wondering if there are any reliable websites or books that can help me get a better understanding on how to properly "predict" (loosely used) an upswing or downswing of a market. I want to get into single-family unit rental units but before I go in I want to be as knowledgeable about the market and how it fluctuates as possible. 

Also, any good websites to see what properties go for in a particular area. I heard Zillow is not that trustworthy and their numbers can be as much as 15-20% off the actual market price.

Thanks for the feedback!