Well, here's a guide on how to make your own files (with a focus on pad files, because that's what I do). I'm not going to say “make your steps like X when the music is like Y” or anything dumb like that, of course. If you want to understand the design philosophy behind Anarchy, go to the “design” page. This isn't about that, though.
The simple breakdown is like this:
First off, I think that any person who makes files should be pretty familiar with the game itself. Basically, I hope you've played enough DDR that you can at least play 9s comfortably. If you've been playing for a long time and can't make it there, maybe because of some physical condition, well… fine, but don't make files too much harder than you can actually play.
Basically, it's important to have played enough DDR that you know what DDR steps should look like, and that you can make sure your files are enjoyable by playing them yourself.
A “proper” DDR song has a good beat (and steady BPM, at least for each segment of the song) and usually a fairly simple melody. If you think you can see people dancing to it in a club, it should be fine. If you can't, it might be okay regardless, but if it doesn't at least get your feet tapping, it's probably a bad choice.
Two things: First, you want to get the basic flow of the song stuck in your head, and second, you have to be sure you really like the song. If you don't like it, your file will come out crappy. That's just how it is.
This is simple enough to do, though. Just loop the song for 2 hours or so, preferably more. You don't have to give it your full attention during that time, go browse the Internet or whatever. What you'll end up remembering probably isn't where every note of the song is, but where the points where arrows should be placed are. Maybe you'll be tapping your feet to the music, or you'll just see it in your head. It sounds complicated, but it isn't, it's automatic.
If you know the BPM already, good. If you don't, go find it with TapTempo or MixMeister BPM Analyzer. Divide 60000 by the BPM to get the number of milliseconds in a beat. Make sure that any amount you cut the song by in milliseconds is divisible by that number (i.e., it should come out to an integer). That prevents the song from desynching when you cut.
All you have to do is match parts of the song that correspond to each other (that is, they sound the same musically) and delete everything in between. Make sure you round the distance to the nearest beat, and everything will come out great. Ideally, the song will end up from 1:20 to 1:50, but if you go outside a little, no big deal (or maybe you just want it to be a different length, up to you).
Not gonna talk too much about how to use Photoshop here, I'll assume you know a little about artwork already. To avoid making unfitting artwork, make sure you're listening to the song as you make the art.
To find stock photos to use as a base for your art, try Google Images or sxc.hu; search for any words that come to mind as you listen to the song, and pick mid-large images (at least 640×480) only.
Yeah, just go make the steps. Maybe you think that because this is what the tutorial is really about that there's more to say about it, but it should come out automatically. The rhythms should already be in your head from listening to the song a lot. If coming up with patterns is giving you trouble, or you're not sure whether you've made the pattern right, pretend to play the steps while you're sitting in your chair. If nothing awkward happens, it's fine, if you're getting a lot of (accidental) doublesteps and other mistakes, go fix it up.
And that's it! Nothing hard, really. If your files aren't coming out great right away, don't fret, you'll get better with practice.