overriding default color order and linetypes

I am trying to create plots that look good in color or grayscale (I
had asked about this before and was trying to write code with a switch
- now I just want decent looking plots without having to switch - and
I never really finished the with switching stuff either).

I use the pylab interface and rely a lot on the default behavior for
incrementing my colors when I overlay plots - i.e. I call plot
different times with different data and it automatically makes the
first one blue and the second green, ...

How do I change the default color order and how do I set up a similar
default linetype order, so that the first call to plot generates a
solid line and the second a dashed one (for example).