For me these are:
- Duplicating content.
- Not using analytics to know what converts.
- Bad backlinks.
- Not promoting posts.
- Ignoring image optimization.
- Not optimising on local search.
- Not using anchor text for internal links.
- Focusing on link quantity instead of link quality.
- Not having unique meta description and title tags.
- Not using available keyword tools.
Can you add anything else?