There's a preset for line-art (as one other answer shows), but for all kinds of refinements, you need to open the whole panel and perhaps also the Advanced settings in it.

Don't forget to check the Ignore White" option. I find it very strange that this option is switched off by default. If you leave it off, you end up with white parts (overlapping black ones), in stead of transparant areas.

Read more about all the Trace settings in this Help page:
How to edit artwork in Illustrator using Image Trace.

Oorspronkelijk geplaatst op Quora: What are the best settings in Illustrator's Image-Trace for line work?"