You need a reliable host for starters! There is no point in doing all you can do as a developer / designer, and then your cheapo hosting company goes down for a week, or takes forever to load a page. Your website needs to be reliable, or else people are just going to give up on it and head elsewhere. Having a website which is light on ads, and high on content is a good way to keep visitors on your site for a long time. Sometimes it can be just one annoying little thing, that you and me mind harmless, but it completely turns a visitor off the site. For me, personally, it is background music!
You want to refer users back to your own content rather than to someone elses as well so if the users reads and article on X, you can try and related them back to article Y via some related post links at the bottom of your content page.
Having relevant keywords is also super important, because if someone visits your website for, example, Apples, and your website is about Cows they are going to leave pretty fast!