01
if you think you can "do SEO" once and be set for life then think again. search engines constantly update their algorithms, and your competitors are always tweaking their SEO strategies. to stay visible you need to keep your content fresh and your site optimised.
02
being number one on Google is great, but if your content doesn't meet the needs of your visitors, they'll bounce. focus on providing value not just climbing the search engine rankings.
03
cramming your pages with keywords used to be a tactic, but now it just makes your content unreadable and can actually hurt your rankings. write with humans in mind first and search engines second.