The first thing that needs to be chosen is the base shape for your earring. You can use a circle to keep things simple. To start make a 2D sketch of your base shape in your 3D CAD program.
To create the spiral shape we will be creating planes that are evenly spaced in height and making a drawing that moves the base shape to different locations. To get the spiral shape we need to draw several of these base shapes at different heights and then connect them to form a spiral strand.
After you have drawn all the base shapes you will need to use the 'Loft' tool. It may be called something different in CAD programs other than Inventor, but it basically connects all the spaced base shapes you have drawn into one continuous strand.
Next you will need to revolve the curved strand you have just made. You can do this most easily by using the 'circle revolve' tool. Click on the 'Circular' tool in the 'Pattern' section, then click on your strand. Now you will need to pick the axis to revolve it around, it should be the one that goes through your first and last layer.
At the top of the earring you will need to make a small loop to attach your earring to. Find the plane that cuts your design in half, hot dog style and make it visible. You will need to convert your file type from your finished 3D drawing to STL (most likely this will work but some printers use other files). You can do this by going to save as and clicking 'save copy as' and then selecting STL as the file type when prompted.
Next go to 'Move' and make sure it is on the build plate by clicking 'Place on Build Plate'. You can also change the size of the object by going to 'Scale'. Next you will need to click 'Export'. Now you will need to get an earring kit from a craft store. They're pretty cheap and have hooks and little rings.