1) QUICK FOLLOW-UPS
When you make your first sale, follow-up with the customer. You could follow-up with a "thank you" email and include an advertisement for another product you sell. You can be more subtle including the offer within your signature file.
Another way is to take your customer to a "thank you" web page right after they order. You should thank them for their order and next begin to tell them about another product you sell. You could also include a picture or graphic of your product.
2) UPSELL ADD-ONS
You could upsell to your customers. When they’re at your order page, tell them about a few extra related products you have for sale. They could just add it to their original order.
Besides upselling on your order pages, you could give them a choice of a basic or deluxe edition of your product right in your sales letter. Your deluxe edition would include add-on products with a higher price.
3) REBATES FOR SALES
Tell your customers if they refer four customers to your web site, they will receive a full rebate of their purchase price. This will turn one sale into three sales.
An additional option would be to give your customer a rebate on one of their products if they would buy two extra products. This type of rebate can double your sales.
QUICK READ SUMMARY
1. Follow-up with customers to sell extra products using "thank you" e-mails and web pages.
2. Upsell to your prospects with differently priced packages and product add-ons.
3. Give your customers rebates for their purchases when they buy extra products and give referrals.