I recommend you to download the GUI interface for potrace and autotrace, which contains two algorithms for tracing bitmapped images. It collects informations in an easy way (hopefully) and then it launches potrace or autotrace with all the relevant options. Using a GUI sometimes is more comfortable that using command line, it is more interactive, and it will easy for you to try different the settings.
How can I improve the quality of the output of Potrace?
The most effective way to do so is to improve the quality of the input!. Scan your image at a higher resolution. Scan your image in greyscale, and use a program such as mkbitmap to generate a high-resolution bitmap to trace.
In some cases, it also helps to decrease the resolution of the input image. If the resolution of your input file is incredibly high, the output generated by Potrace might be larger than necessary. This also sometimes happens if the input is speckly or noisy. Rather than trying to simplify the vector image, it often helps to just downscale the input bitmap.
There is an utility called
mkbitmap which converts color or greyscale images into a format suitable as input for other programs, particularly the tracing program
Potrace. It is particularly useful for converting scanned line art, such as cartoons, handwritten text, etc., to high-resolution bilevel images.
In this website you can find some examples of the operation of mkbitmap.