I agree with many replies above, and I actually do understand what you mean by contradicting information online on search engine optimization (been there and done that, and I was in the same position as you many years ago) and there came a point where I had to re-evaluate many seo information that I sifted through. I had tried all the methods above, and similar to you, I had to rely on my own research and testing.
All the points you mention "directory submission, article submission, social bookmarking, blog commenting and forum posting" is useful, with exception being "blog comments and forum posting" because these two options should never be attended just for the sake of back-links. Meaning, if you really enjoyed a blog post and sincerely want to add your comment then this is a good way to build relationships online, but if you just want to get a mere back-link from a post then that is negative approach. Forums are a good way to build relationships and share your expertise and passion with like minded internet citizen, but
once again, never participate in any forum just for the sake of back-links (if they offer it like this community at v7n) that's great and is a bonus.
I would also encourage you to focus on article submission a little more than directory submission, because I found this approach one that is, one the best (and surely social bookmarking go hand in hand with article submission) also allocating time to relationships with FB, tweeter, G+ are all good as well.
Basically, keep in mind to get people to read what you communicate (and when you have your readers best interest at heart, and build your presence online as an expert, then search engines will rank you higher naturally) because people need to follow you, and search engines follow people
Now comes a tricky part, since you have experience of internet, then I will tell you, that if you are serious to learn the best search engine optimization tactics, then it is only intelligent to research and get to know your target better (to understand what it is, how it works etc) Google never tells all, nor reveals it all, since Google is a business, it is also important to keep up to date with this giant (its business deals etc) meaning, recently they have invested very big, in mobile phone market, this will mean staying informed with mobile site and search engine optimization implications of this evolving behavior.
What I found was that learning through w3 schools and web semantics are extremely helpful for becoming a seo specialist (here's a link http://www.w3.org/standards/semanticweb/
) since we are dealing with computers, data, programming, and most importantly, language
since words are the only real currency on the WWW (where would we be without them?)
You can also look into Google beginnings, and read this The Anatomy of a Large-Scale Hypertextual Web Search Engine
you can also search YouTube with this term "google mapreduce lecture
Stay at it, and before long you will work out what works best for your seo projects, because depending on what your online mission is, what may work best for my online mission and seo requirements, may not be the best approach for you, and vice versa.
Keep in mind that foundations do not change, and once again, always have your visitors best interest at heart, then naturally build your online presence and back-links.
I sincerely wish you enjoyment in your learning (because, you need to enjoy this stuff to be the best in your field)