Looking to start my own property management company. Any books/memberships to join for landlords?

[Manuel Sarabia]

I'm looking to start up a property management company in my area as I believe it's a good opportunity. I have a few rental properties and have been doing my own property management for about 4 yrs now so I have a decent idea how it works. But I want to expand my knowledge as much as possible to be able to manage on a very large scale. Any books I can start reading or memberships/clubs that cater to property managers?