I think success depends on whether the issue is a little gum/buildup, or major crud (rebuild).
I haven't done it often, but for minor issues, the two ways that I have done it is either adding SeaFoam to the oil, and using SeaFoam top end cleaner in the intake, or to use EPR's magic additives ($$). Generally they have worked for me on engines where a PCV or EGR system had an issue, so basically a good engine that started consuming oil. They got cleaned up, and went back to not burning oil.
All the best,
2Pbfeet