Consider your Audience - start with your reader when considering what to promote. Relevancy is key. Genuine Recommendations and personal endorsements always work best - recommendations of things you personally genuinely like are always best.

Link to Quality Products - the better the products that you recommend the more your readers will thank you for suggesting it. Contextual Deep Links work Best - in general you’ll have more luck promoting a product from within a post than on a sidebar

Consider positioning of links - links/banners that are in parts of your post/blog that where readers look work best (top of posts for example). Traffic levels are Important - the more eyeballs your promotion gets the better.