How much security deposit to ask for?

[Rolando Frias]

I am in the process of putting a single family home for rent. We are not sure how much we should ask for as a security deposit. We are thinking first month and also a deposit that is at least $500 over rent amount. We have already had a past tenant tell us to keep the deposit as the last month rent and then left us a mess and several repairs.

What is usually seen as common practice? 

Thanks in advance