Present your items clearly so that a visitor to your site immediately sees what you have to offer, and the prices.
Allow the visitor to navigate your site without getting lost, or strange things happening. Use few pages rather than many.
Make it easy for the user to select items
Calculate all the prices - total item price, shipping, sales tax where applicable.
Validate as much of the information the customer has provides as possible. For names addresses, at least check there is something there. Phone numbers can be checked for the correct number of digits.
Make it easy for the customer to pay. Accept credit cards, by far the most satisfactory option. Checks, money orders, envelopes, stamps, post offices, time are all obstacles to making a purchase.
If you want a customer's credit card information, you must provide a secure way send that information!
Provide an order number. It is useful for both you and your customer.
Provide your phone number, email address, street address.
Remind the customer to print out a copy for his own records.
Thank your customer.
