Did you have in mind a fantastic design for a ring that you'd like to 3D print? Perhaps you'd be interested in watching a 55 minute tutorial on the basics of 3D jewelry design, specifically for 3D printing.
The tutorial uses the open source 3D design tool Blender, which is available for free download.
A word of caution: Blender is noted for its difficult learning curve. However, for some its price (free) may override such challenges. In any case, tutorials are always welcome, aren't they?