I agree with above two posts. You want NO pressure. If you are having to use any pressure to get it to cut then your razor is the culprit. That's how you get irritation and razor burn. A sharp blade should just slice right through, no tugging, pulling, or skipping. As far as the angle I think lowering the angle closer to your skin on XTG and ATG passes might have something to do with minimizing irritation also. If everything is right the blade should cut with no pressure and irritation. I'm still not brave enough to try ATG on chin and mustache, just the neck and under chin for now.

Check out the Wiki on guillotine and scything strokes also. But it might be better to wait on those until you are comfortable with regular strokes and have a sharp razor.