Quality of your content. This is one of the keys. You should also remember that placement is crucial. Your seo-friendly content should be somewhere near the top of your website. It's good if you have some photos you want to share or a nice logo, but find some space for the text as well.

When it comes to pictures, you should keep the balance. On the one hand, you shouldn't use just text, but on the other hand don't exaggerate with pictures, text is much more useful in terms of seo.

Since the pictures themselves are not recognized by search engines, you should use alt tags and give proper names to your graphic files. For instance, if you're selling fish tanks and have one on your front page, you might want to name one of them fishtank.jpg.