There's a couple of ways I like to do it, and all them follow, of course, the perpendicular line I've been talking about. The first is an advancing form. This is the only video I've found (so far) of it.
Basically, you step with your right foot across your left and next to uke's right foot. In the video, the guy throw largely straight back. I prefer, however, to turn uke's hips and shoulders a little (with the elbow draw) to align with his feet and throw at a slight angle, about 35 to 45 degrees. Here's the set-up:
I've found you can also approach it similar to the way we do okuri ashi harai (step around double footsweep). Pre-turn either foot, off to the side, so you have three feet on a line. As uke's back foot comes traveling forward, your do a quick exchange of your own feet (as in kouchi gari), so that your left foot (or the foot closest to uke) step onto the new line, the reap with the outside foot.
I know, I know. Kind of confusing. I need to take some video. One of these days.
Incidentally, you can load osoto gari the same way, only without the quick foot exchange.
At any rate, that's all I'll get into for now. But I have to say, this idea of what I call "squaring up" with uke (getting his hips and shoulders lined up with his feet and directing energy perpendicular to that line, off his heels) has all kinds of implications, not just in judo, but aikido, too. I mean, the more I think about it, the more I see it in aikido, starting with good ol' number 1, shomen ate. But I guess that's another post for another time.