Start by cleaning your glass really well with alcohol. It is best to do this to any glass before painting it.
I had a glass painting kit from Decoart that had these cosmetic sponges already in it but you could pick these up anywhere. Just dab on some of the frosted gloss enamel.
I just eyeballed the lines and started applying the paint. Keep brushing down with your sponge until the paint is nice and even. These enamels dry really quickly which is another great thing about these paints.
Then just continue up the jar with your other colors. Obviously my patriotic mason jar used red, white and blue.
I also made a rainbow themed mason jar while I had all of my paints out. I am telling you this project is so simple you will make a dozen before you know it.