I find that as I am painting my figure (face) the oil paint leaves very small bits (dry paint?) How do I avoid this I'd like to get a smooth surfcae should I be thinning the paint a bit? I use straight out of tube.

Here are a couple of guesses:
Firts, have you used these brushes before? Specifically, have you used them to paint with model paints? I've heard that you should never use a brush with different paint mediums.
Second, what brand of oil paint are you using? It could be the pigment in the oil paint itself. Look for the finest quality paints you can afford. I try to use Winsor & Newton Artist Series as opposed to their regular, lower priced series. I think the pigment is supposed to be ground much finer.
I hope this helps,

Despite what others say, I always thin my oils. To help smooth them out, you might want to try a bit of Liquin, available where you buy oils. Seems to make the paint flow more smoothly.