If you had one trick to share for SEO, what would it be?
There are no real "tricks" per se.. everything anyone needs to know has been posted about, blogged about, written up in articles, magazines, etc. It's everywhere. It just depends on what YOU want to believe and actually put into action. A lot of them take time to do, so people try and find shortcuts. The more shortcuts you use, the worse you'll do in the longrun.
Here's what you need..
1- Good titles
2- H tags (people may disagree, but they still hold value, even post-Florida)
3- Relevant one way links from relevant sources that have some type of TRUST. Getting links from every site in the world related to your topic is good, but it's a quality over quantity game.
4- Unique content with keywords. This doesn't mean to sprinkle a few or bombard it with tons of keywords, it means keep whatever the topic of the content is ON TOPIC, not on something else.
Those are my favorite 4, and probably all you really need in the long run, in spite of any crazy changes. This will work on Google, but also on many other important engines both nationally and internationally.