Nobody to mention split-testing ? Old school approach but extremely useful to find out what landing page is converting best.
Make few landing pages around same product, each of landing pages to be different (colors, fonts, buttons, call-to-action text, image position, headlines, etc) and drive/pay traffic to randomly chosen landing pages. At least 10k views would be nice.
You would be surprised how actually just one of LP's is getting 70 % of sales and conversions, and others perform few percents or 0%.