Tracing a bitmap -- quality terrible...what am I doing wrong?

[Glenoran1]

I have hundreds of bitmapped scans of hand-drawn designs I'd love to trace, but the quality comes out like this (or variations of this, as I tweak the options). The first is the original bitmap, the second is the traced version.

Can anyone please tell me how to get a 'clean' tracing? It becomes even worse when I have a coloured (filled) design.

Many thanks for any advice you can offer.

Regards,

Glenoran1