Drawing on Fabric
If you have a sketch in pencil or crayon, you can easily transfer it to fabric. As a base fabric, a plain 100% cotton fabric is perfect, I get mine from a stall on Leeds market. To make it easier to draw on fabric, either tape it to the desk using masking tape or iron it onto freezer paper.
Derwent Inktense Pencil Crayons
These crayons are widely available, I think I got mine from WHSmith. They are really easy to use and give a similar effect to watercolour crayons on paper. They can be used for really detailed drawings. Tape your cotton fabric to the desk and use the pencil crayons directly on the fabric. I have used ordinary pencil crayons, but the Inktense crayons give a much better colour, especially if you use them wet, or wet your picture afterwards with a paintbrush. You can see them used for a quilt on the Inktense crayon page.
Caran D'Aché Neocolor II Watersoluble Crayons
Also widely available, these give an effect more like using wax crayons or pastels on paper. They are better for covering wider areas than for detailed work. I created a version of my Daffodil quilt using these crayons. They were easy to use and when I sprayed the final piece with water it blurred beautifully to give a watercolour painting effect. You can see more detail on the Caran Daché Neocolor page.
You don't need special crayons for fabric, it is possible to use ordinary wax crayons like Crayola. I used wax crayons to make a russian doll picture. This really is only for art quilts and I wouldn't want to use my sewing machine to stitch into the wax areas. It is great for hand quilting and fun to do. Have a look at my Russian Doll postcard quilt.