That's a question with a lot of answers, and many of them will depend on the type of style you're looking to attain. Personally, I'm a big fan of using the Crayon tool (with it's softness set to 100%) to smear the Oil paint. I also like switching on the Oil paints Insta-dry setting, and using a thinned paint (about 90% thinner setting) to layer the colors, until they blend out. I explain more about this here: Link.
If you're looking for a purely flat image, you might want to turn off the light rendering, on the Canvas Panel (View > Canvas Settings, and then click on the Light bulb icon).
(Edit) - One more Link
Last edited by Someonesane; 05-25-2012 at 02:14 AM.
Nothing is easy to the unwilling.