I highly recommend reading
What No One Ever Tells You About Real Estate Investing. This book gives a good overview of the problems landlords face.
This is not to discourage you from becoming a landlord. Rather, the more you are prepared the more you will weather any problems well and come out with more profit.
You may want to read a post from my Home Finance Site on Renting. My fellow editor, Dianne, shared her experiences with renting out her house. Here is the link:
Home Renting Pros and Cons