The first thing is to understand the format of the definition file
for page in visit("""<a href="(?<content>[^"]*)" rel="next">"""):
foo = download("""src="(?<content>http://www.commissionedcomic.com/comics/[^"]*?)" """)
The comic part helps name the definition (and the folder that it puts files into).
The start_at tells woofy what URL has the first comic (you can usually get to this by going to the comic site and clicking the first link) in the case of your first comic it would be http://www.accidentalcentaurs.com/?webcomic_post=2010-01-31
The next part has two important bits that you will fill in the blanks for, the first is the "next" link url, and the second is the image link content.
Now, the regex might scare you a bit, but my example above is about the easiest one to use. So visit your acciental centaurs comic and right click on it. Then click on View Source. Now you will see a bunch of code, just hit Ctrl + F and do a search for the word next. In the case of accidental centaurs, it is contained in the line like:
<a href="http://www.accidentalcentaurs.com/?webcomic_post=2010-02-20" rel=next class="next-webcomic-link next-webcomic-link-12 webcomic-kbd-shortcut"><span>Next ›</span>
<a href="(?<content>[^"]*)" rel=next
Is what you would want for the regex.
The next would be the comic link. Look at the source again, this time for the image tag. It would look like this:
We need to make a regex for this
Save the file and have it end with .def
So it will look like:
comic "Accidental Centaurs"
for page in visit("""<a href="(?<content>[^"]*)" rel=next"""):
foo = download("""src="(?<content>http://www.accidentalcentaurs.com/wp-content/webcomic/untitled/[^"]*?)" """)
Then you have to test it. This is the tricky part. Just let it run and if it breaks, try to figure out where it broke.