Several months ago (many) a friend recommended me a guide, which I started looking but did not manage to find the time to actually read it carefully ,the guide is “Dive into HTML5“, and I must say that is one of the best guides I ever read. Normally I get bored with guides and begin skipping things or jumping from one place to the other, but this time I really enjoyed reading it carefully, page by page.
It gives a really good overview, deep enough to understand and implement things, and lightly written to actually catch your attention, so I highly recommend reading it.
Of course, procrastination is part of the reading, so in the way I found other resources that had to do with HTML5 that I find interesting.
If you are semantic fan, as I am, making the UI semantic is really interesting, and there is this semantic UI , which helps to give semantics to the front-end, and of course there is a gem to use semantic UI in rails, the semantic-ui-sass gem. Also you can find a podcast in The changelog about Semantic UI with Jack Lukic.
Another of the amazing things, refered to semantics is that HTML5 gives you the possibility of extending semantics through microdata, and there is already a microdata vocabulary initiative for defining the most common things, data-vocabulary.org, and you can follow schema.org blog for the latests news.
So if you feel that you want to play with HTML5 you can use Initializr which is a templates generator to help you getting started with a new project based on HTML5.