1) Quality Content - Quality content is the best way to get search engines to your web site. Sure meta tags and key word density matters but the best way to get to the top of search engines is fantastic content.
2) Keep it Fresh - Do you still have events, pricing or dates on your site from 2013? Not only does this look bad but harms your search engine placement.
Search engines monitor how frequently you update your web site as they index it and will punish sites that don't keep their content up to date by dropping search engine rankings.
3) Keep your software and plugins updated - Most web sites run using software and software extensions. It is of paramount importance to keep this software current. Hackers use security flaws in outdated web software to exploit web sites running on old software versions. Keeping your web site plugins updated will keep your web site safer.
4) Take backups - Obviously :)
A backup is like a first aid kit, you hope you won't need it, but its a lifesaver if you do.