Topic : The best SEO strategies?

What is for you the best SEO strategy? We all know that organic links are the best but so hard to get. Only websites doing tools used by other webmasters ( i.e. http://www.pagerank.fr used for this website ), successful blogs or breaking news websites can easily get them but for the rest of us, it's another story.
I did try for my part before monthly paid links. It's good for a kick start to help your website do get a decent PageRank to start link exchange BUT if you're too greedy ( I was ), and get caught, it will be a sanction. I'm currently stick with a PR2 ( was PR4 and been drop to PR2 6 months ago ) for one of my websites because of that while since I had some very good link exchange which could put me easily on rank 4.

I'm currently doing triangle linking and so far, it works but I'm not sure if it's as good as a one way links but for sure better than a reciprocal links exchange.
I've heard about bookmarking might be part of the algorithm as well? Somebody had a successful feedback about it? I do use ( http://www.xmarks.com/ ) but not for long enough to knows if it's work well.

For directories, only those with big PR, hard links, deep linking allowed and with contents really helps but for those not using all or part of that, it doesn't even worth to add your website.

Then, WHAT REALLY WORKS FOR YOU?