1. I bought Oil-based sharpies from Michaels. From what I've read if you use normal sharpies it will eventually just rub right off. The Oil-based sharpies come in different sizes. I bought the fine point and medium point markers. I found that the medium point were easier for me to write with, but I really think it depends on the person and the design.
2. I washed each mug and then wiped them down with rubbing alcohol and let them dry. When they were dry I started drawing on them. It takes a little bit (especially if you are not an artist and I am not one) to get the hang of drawing on a mug. If you make a mistake (I made lots) you can remove your mistake with nail polish remover.
3. Once you finish designing your mug let it sit for 24 hours before baking in the oven. After 24 hours place on a cookie sheet and put the mug in the oven before turning it on so that it can heat up with the oven. The first time I turned my oven to 450 degrees and after it preheated, I baked the mugs for 30 mins. This worked fine for the the mugs I drew on with the black marker. However, with the colored markers it distorted the colors at that temperature. (see below).
See how the colors faded :/
So I tried it again and the second time I turned the oven to 375 degrees and baked for 30 mins. and wha-laa...The color was not distorted. (see below)
This was Brian's birthday gift from the boys this year ;)
4. After the mugs bake for 30 mins. turn off the oven and let the mug cool with the oven. I waited about 15 mins and then cracked open the oven door and let it finish cooling. After it cools you have a brand new really cool personalized mug! :)
I would advise hand washing the mugs. I read that after doing this you could put them in the dishwasher and they would be fine, but I don't know if I'm convinced. So be cautious about how you decide to clean the mugs. I've hand washed all of mine and they have been just fine.
I purchased most of my mugs from Walmart. They are under a $1 and seem to work great for this project.