In this post are additional resources that you could use to enhance your understanding about SEO.
Feel like going bit more advance on SEO? Here is Google's SEO Starter Guide. It contains the A-Z of SEO for Google.
Reading materials that are commonly used by the SEO community:
1. Google's official blog
It's always updated, it's always correct, and it's always something you should be reading. However, this blog is purely for the latest news from Google. You won't find them giving tips on subjects you want to learn more about. For that, you have to read the others.
2. Search Engine Land
Arguably the most popular SEO blog around, this one seems to have it all. It is always the first to break news, and you'll find that they have several articles on one subject, so all of your questions can be answered right on this blog. You'll find that most of the writers are the same each day, but the topics definitely have good variety.
3. Search Engine Watch
This is also one of the main blogs out there on the web for SEO. This is probably one of my favorite sites to navigate and one of my favorite designs. While Search Engine Land is typically the first to break news and get it out there, Search Engine Watch still covers the news and always seems to publish just a little bit more frequently and add just a little bit more information. In other words, reading both is beneficial.
4. Search Engine Journal
This blog thrives on guest contributors, so you're always getting different topics and different voices. It still covers news like the other two main websites, but this one seems to have a little bit more fun with videos, great comments, and some of the most detailed content around. Note: I'm the Editor at Large of this site but I still think it should be on the list!
MOZ has been in the SEO game since 2004, publishing some of the best guides available for beginners. They also publish quite a bit of advanced material and keep things very detailed, so just about any small business can benefit. They don't report SEO news quite as much as the others, but they delve into popular topics frequently.