Losing an email list can cost thousands of dollars as well as months or even years of hard work. Carefully plan out how often you want to send users emails. Try to add something of distinct value on the subject that you are emailing them about. Make personal recommendations on selling products to them and try to do so only once you know about the product. Do not simply promote a product because it has received a good response rate elsewhere; promote it because your list is interested and ready to spend some cash!