A small cheat that I use when painting wine glasses, is by printing out the image that I want to paint onto the glasses (this time I also printed out 'Merry Christmas'), and tape/blu-tac it to the inside of the glass and 'colour in' with paint. You can work out where you want the images to go before starting as well (if you are a symmetrical and perfectionist painter like myself). And any small bits that go out of the lines can be covered up with a black outlining paint pen anyway - Phew!
In the lead up to Christmas last year, my children and I painted wine glasses for some family members. It was such a fun thing to do (though I forgot how time consuming it was). This year, with the inspiration and motivation that came from the creativity seen at the ladies craft morning (and the fact that a couple of family members were at the craft morning), I've decided to paint some glasses for my children's class teachers.
The outlining paint pen also gives definition to things you are painting, and made a huge difference to the Hollies that were painted onto these wine glasses.