First, I would suggest you to pick a program. There are lots of programs out there that you can use to paint digitally. I would suggest you to use Paint tool SAI because it is very user friendly, so you're less likely to get stuck on a certain part of the process. Next, when you're actually painting, don't worry too much about making it perfect. If you want to be perfect, you're going to spend a lot more time than you want to be. So, use the painting tutorial to get an idea of how the line work should look, and then go crazy with it. Then, when you're finished, you can call it good and it's really that simple. You don't have to be a digital artist, you can just be creative with it that's it!