German microphone brand Neumann have put together a series of tutorial videos on recording and microphone technique.
So far there are 5 videos in the series with many more to follow I am sure. In the series there are two covering recording vocals in a home studio and 3 on recording acoustic guitar.
Neumann & award-winning filmmaker Geert Verdickt is a fantastic host for these videos which are obviously geared towards Neumann mics but the techniques shown will work with any mic brand of course. At times these these videos can be quite basic stuff but forget the basics at your peril.
The Neumann Academy is also a fantastic place to learn more about how microphones work and some of the technical terms that are used when talking about microphones like Impedance.
Check out the Neumann Academy here.