Best thing to do with cash flow?

[Vincent Plant]

I just picked up my first rental income property. I am in the process of having it rented out and have a tenant scheduled to move in within the next few weeks. 

If everything goes the way it should (the tenant pays the rent with no issues and no surprise repairs come up) I will be on track to begin cash flowing $650/month. 

What would you suggest is the best thing to do with this income? I plan to stash 10% into a side account for any issues that arise. But what is the smartest thing to do with the extra cash? Put it back down on the on principal? Pay down other debts? Use it for the shopping bill? 

I intend to purchase another property as well in the not so far future so perhaps stashing the money to plan ahead for this? Im all ears...