Selective Colouring 101

Yes, I know some will say trial and error, that's fine if you don't suck at photoshop and aren't a complete nube BUT is there some kind of tutorial that gives you the basics on selective colouring?

A jumping off point to start negotiations with your own experimentation?

Just to be specific. Where to increase/decrease a certain colour or blend certain colours to get a specific colouring just in general because I know all pictures are going to be different.

Just something general like I've seen for cropping, blending etc tutorials for beginners.