I've been spending a fair amount of time working with microdata recently and I've found this Google Structured Data Testing Tool an incredibly useful to have a tool to help me test whether or not my markup has been correctly written.
This post from html5 Doctor is more than four years old, yet it's still one of the best resources on microdata that I’ve found.
Here’s a brief introduction to the concept of microdata from Google. It’s a nice resource with a handful of examples attached. SEO is definitely something that microdata improves so info coming straight from the horse’s mouth is something we should pay attention to.