that's a very broad question, unfortunately...my sort of off-the-cuff answer is that if you want to advise others about seo then you need to read everything you can get your hands on so that you can answer any question. if you want to just make your site more optimized, then get a book like this and read up and put in place what he suggests...
If you want to be an SEO pro you are going to need to do a lot more than read a book or two. Although that is absolutely helpful, you are going to have to have practical experience and a lot of it. That is what will make you a pro.
I would suggest that you start a few sites and read everything that you can about SEO and use those techniques on the sites. Try some things on one site and some things on another. Use what you learn from this on other sites and on clients sites. Over time (lots of time) you will gain the experience needed to be a pro.
A good book like what has been recommended here (I have not read it myself) will give you lots of tips and shortcuts, but book learning is not a replacement for actual "real world trust me I've been there see here are my examples" experience.
You need to understand that SEO work is time consuming and takes a lot of time to see results. Search engines are slow to respond (read this as months or more) so changes to your site will have to be looked at over a long period of time.
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