I recently visited a local winery for a wine glass painting event and look what I did:
There was an art teacher there to walk you through different technics for painting flowers but overall you could do what you wanted.
If you are interested in doing any of your own glass paintings, here are the basics you need to know:
1. Clean glass with rubbing alcohol before painting.
2. Use enamel paints.
3. To set paint - put glassware in a cold oven, heat to 350 degrees, bake for 20 minutes, turn oven off and let glass come back to room temperature in the oven.
4. Handwash glasses.