Ring of Fire climbs up just left of center of the face immediately to the left of the Combination Blocks. The very well-protected crux comes about 1/3rd of the way up at a small overhanging section, which is then followed by consistent 5.10+ climbing to the anchors.
If you study the holds from the ground this is a great opportunity for a 5.11+ onsight.
One sidenote: I had a belayer drop me to the ground on this route once-- too many people chatting and not paying attention to me while pulling through the crux. The boulders at the bottom don't make for very good crash pads. Smith Rock can have a very active social scene and it's easy to become distracted. Pay attention to your climber!