SEO-What is it and how do we DIY?

I am very interested in DIY SEO. I have done a lot of reading and trying to implement this on my own but I am failing. Henry17 commented in another thread that SEO firms are a scam and overcharge for something that can be done on your own. He is probably right or at least close to right and I am interested in hearing what he and other people have to say. There is just way too much on the internet to filter. Hopefully we can do it all here.

And go...