For thinning, ordorless mineral spirits work fine...

As far as technique, it depends what you are doing.  For a pin wash you use them the same as you would anything else...  I use them for pin washes and to create oil streaking on wings etc.  To do the oil streaks, I thin some down and dab them onto the spot where I want the "leak" to start, let them dry a little (1-2 hours) and use a cosmetic sponge to smear the oil back in the direction of the airflow.  Make sure to do it on a gloss coat though, it can be near impossible to remove if you dont.