I tend to just do it on what I am drawn to in nature. When I'm out walking etc. I don't really do anything special as such, just find a tree or rock that I am drawn too and place my third eye on it. Then as you say just focus with your third eye, I do reiki so I also channel through those energies too but I sure you don't need to do this, it just an added perk :)

As for the crystals I'm not sure, just again what I'm drawn too. Try getting the Crystal Bible good description of crystal powers in that :)