INVOICE MORE OFTEN

Billing just once a month and not getting paid and then waiting another month to bill again?  Boo on you!
Bill as soon as the work is performed, bill two weeks later, and then if you don't get paid at the end of the month, give them a call, and if necessary keep billing every two weeks until you are paid, or until you sue the bastards.  Bill more often, get paid more often. Sound good?