They often say, learning new things is way easier than unlearning old things.
A WebmasterWorld thread has an old SEO who hasn't been in the game for five or more years, asking to be caught up quickly on what has changed.
The answer is, a lot. With all the various algorithmic changes at Google around Pandas, Penguins, Hummingbirds and so on, things have changed.
No longer is it easy to manipulate Google based on their ranking factors, now you need to be real. Here are some quotes from the thread that stand out to me:
Put your users first. Make your site as USEFUL to your users as possible.
I don't focus on "SEO" and do OK.
Things of the past to no longer do: Press Releases (Panda victim), Keyword stuffing, source code order, footer links, site wide links and being unconcerned about page speed.
It is often amazing looking back at how far SEO has come, how Google has forced it with their algorithms, for better or worse.
Forum discussion at WebmasterWorld.
Image credit to BigStockPhoto for seo image