I had a hard time dealing with incoming orders and remembering who paid when and so on. You probably will too. So I asked around the forum, got great help from cindy and other sellers, and eventually came up with the following technique.
Have your email inbox set up with several different folders. I have the inbox for pending orders, epayments, and requests folders to name a few. As soon as I answer a question not involving a pending order I move it to the corresponding folder.
When I recieve a payment electronically I write down the order in my notebook and list all important information, then I add the item to my google calendar which keeps my customers up to date on their orders.
When I recieve a snail mail payment, I write down the order in my notebook and list all important info there and on the envelope. I then add the item to my calendar.
Then I just wait until their order is up, take pictures, email said pictures, package the item and go to the post office.
Sometimes I realize an order has been in my inbox for a while without payment. Usually I give a week or two if I bother and send the customer an email reminding him of payment.
Easy as pie.