Usually I have an overall idea, do a kind of straight-ahead pass for the key poses (but with a general plan in mind), and finish up by inbetweening those key poses. So, both?
This one, however, was pretty much straight ahead as it was just a doodle. I had no idea what I was going to do until I did it. I did go back and add some inbetweens to smooth out and improve what I had at the end, though.