1.Animated ads. For example, ones that fly around your screen.
2. Pop ups. The reason why you should not have pop ups is that if people are using a mobile device then your site will not display properly, or it will not show at all.
3. Blinking text.
4. A hard to see background on hard to see text. For example, yellow on pink background.
5. Hidden text.
6. Excessive use of images. ( Too much can use up a lot of bandwidth and can increase the page load time.)
7. Don’t present your important content using multimedia.
8. Avoid making multimedia elements play automatically.
Tell us what things you avoid on your site in the comments.