Originally Posted by AwesomeAssistan

I usually charge by the hour, on a retainer basis. My clients pay for XX number of hours per month, prepaid. I always get a signed contract and a check before I begin work. Then I just send an invoice the first of each month for that month's retainer fee. If there are overages, they get billed at the same time, with payment being due within 10 days.

This is exactly the method I have been considering. Has it been working out well for you?