How many SEO techniques do you know ?

SEO is not a fixed science to have X number of techniques. I can broadly divide it into3 as you've already done :

1. What we should do : White Hat

2. What else can be done : Grey Hat

3. What we should avoid : Black Hat

There's a number of techniques and trick we can do  in each one of these categories, but it actually depends on the website and the business it is in. What I mean to say is that SEO is a customized solution, there's no holy grail that "One fits all" type.