The water mixable oils you can thin with water. I like to add a little bit of dish soap to break the surface tension if I'm going to be using it for washes. I prefer the water soluable for a lot of things, but I use both standard and water soluable oils.
You'll want the surface of your model to be fairly glossy before you lay down a wash. do you don't get "tide marks" where the pigment stops spreading on the flat paint and leaves a high water mark.
Mix up a batch that looks about like coffee, then just apply it to all the recesses and inside corners and basically everywhere. After it's mosty dry, you can take a q-tip dampened, and I do mean *dampened*, not wet with Windex (if you're using watersoluables) or mineral spirits (for standard oils) and gently wipe off any excess. The gloss coat will help with that as well. Once it's dry, lay down the flat coat of your choice.
Hope that helped some.
Madda
Trifles make perfection, but perfection is no trifle. -- Leonardo Da Vinci
Tact is for those who lack the wit for sarcasm.--maddafinga