Co-signer on a lease, what parameters do you use?

[Mauricio Quintana]

Landlords,

I have a property i'm renting out and the tenant is having a family member co-sign with them but will not be living in the property.  I've never had anyone co-sign.  What is the value of having someone co-sign?  Does the lease go in both of their names?  What information from their credit report do you give and not give merit to.  Example, co-signer has pets.  I don't allow pets but he won't be living on the property.  

Any insight into do's and don'ts of co-signers would be greatly appreciated.