Ah, this is a problem a lot of people have with flash, myself included. The brush just has a complete mind of its own. Unfortunately, there’s only one setting you can tweak, and even then it’s not the greatest help. When you’re on the paintbrush, you should be able to see a Smoothing toggle in the Properties, which you can set from 0-100. I have mine at 0. Other than that though, there isn’t much you can do other than redoing lines until they look good for you.
Can you please post a picture of your brush settings for Flash (Given thats what you use) On Flash (for me), the brush always seems weird and unnatural and it is KILLING me! I really want to get into small animations, but this problem is stopping me from trying it.