In my opinion, the best way to start out learning how to make cartoon dolls is to making new clothing on bases already provided by other other people, such as myself, and other dollers.
My tutorials here are pretty basic, so if you have never made a doll before and have absolutely no idea how to start, this will get you started. Basically, you are working pixel by pixel until you get familiar with how to draw on the computer, and then you can start playing with various tools in your paint program.
Here, I will, instead of trying to convey the idea of how to create new clothing for avatars/dolls and new doll bodies, I will take you through the process of how I actually make them, one at a time. Here I will show you how I create new clothing, and I will demonstrate using a picture though. You can create anything you have in your mind if you want to as well as using your own drawings for reference.
If you find this easy at any point, you don't need to be reading this and you can move on to making new doll bodies, because you obviously know how to do this very, very well.
Here you can see I have selected a picture that has pretty, not general, but simple, nice looking renaissance type clothing.
I will start by drawing the outline of the dress on this basic body avatar. (Excuse this picture - or lack thereof - as it was damaged and I have to go onto my other computer to retreive it).
Here you can see the outline I have made of the dress. I have also shifted both of the arms; well actually I have created them both, as the one seems non-existant and the other is normally behind the doll.
I do this by keeping both the image I found, and the doll's image both open at the same time, and keep looking from one to the other to make sure you keep the proportions the right way. You can use the paint brush tool or you can use the Draw tool, and make sure in the tool options box you click it on Freehand Line. So you can draw out the line you want to make, and if you mess up you can just undo that action.
I started shading the doll's clothing; remember, use darkest to lightest colors, and try to use 4-5 colors of the same shade, to make the doll's clothes look really great.
I will be adding many more examples of how I create new doll clothing and then on to new doll bodies. New doll bodies are harder to create, and they are definately NOT for the artist who rushes through their work, because in this you have two options: create it entirely by yourself, or shrink down an image, which means you'll have a lot of cleaning up to do. I will start covering this later though, after I get some more stuff done for this web page.
Here is the other way I make new clothing. I take an image and play with the size of it, until it fits just right. I usually zoom in when doing this, because there is a lot of cleaning up to do when you resize an image to such small proportions. You can see the evolution from a real picture to a cartoon doll image along the way.
You can see that I started with an image that I shrunk down in size. I also got a 'prep' doll upper body, and then I moved them into just the right positions to look proportionally appropriate. I then started to fix and shade the colors and render it in the cartoon doll style. Wow lol I sound really technical...I'll try to stop that :P
I just kept going and going with the shading, trying to imitate the shading from the original picture. Just by looking at the pictures you can see how I colored it (I hope), and I will be adding more examples to this part of my web site as well. Its sort of hard to put into words what comes pretty much naturally for me, so I hope you can see from the 'evolution' of this doll how I ddid it.
This doesn't mean you should make new clothing this way for all your dolls, but it's a great starting point. Once you get good at making dolls, you'll start to envision your own characters and clothing. I hope you have fun!