If you use cookies, don't nag your visitors more than once per visit to allow you to set a cookie. That Aren't Immediately Fulfilled You should make some kind of free offer on your site that will allow you to capture visitor names and email addresses. But you should only do this if you can immediately fulfill your offer. Many sites offer free consultations or information, then fail to deliver. This can permanently damage your credibility.
Many sites have non-secure or confusing ordering procedures.
Better to not request credit card info, etc. If you have more than two or three items for sale, invest in a shopping cart ordering system. Make it easy for customers to buy from you. Most people will not take the time to load plug- ins to view or do something at your site unless you give them a great reason to do so. They'll just click away.