These articles/videos say it better than I could.
Good article by Duane Thomas with tips from Brian Enos and Dave Sevigny on gripping the handgun. While they have different nuances of their grip, they both use a thumbs forward, straight thumbs grip with the support wrist bent forward a little bit.
Magpul Dynamics on handgun grip
Springer Precision on handgun grip (check the 2 videos)
Maximizing the Combat Grip by Chris Fry
Check the section about using grip tape to enhance the grip, and where the grip tape was applied
For more technique tips: http://jumpthestack.blogspot.com/search/label/shooting%20tips