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About start a blog there are a lot of solutions for free (see for example Wordpress site).
But there isn't a magic set of tasks to become a vExpert... is not a certification where you have to pass an exam.
Have you seen the previous application form of vExpert? There are a lot of point where you describe what you do.
Blog site, twitter, VMware Community, books, VMUG, ... are just a set of them.
I can only suggest to just start, use Twitter and Google+ (there are a good circle from Jonh Troyer).
Help in the Community, write some post, and so on...
Thanks a lot Andre Mauro!