#Boss Fight

I've been trying to beat the Asylum Demon in Dark Souls for hours now and I just can't seem to get it right. I've watched a few videos, read some strategies online, but every time I think I've got it down, I end up getting destroyed. I'm starting to get really frustrated because I know I'm close, but I just can't seem to execute. Has anyone else had trouble with this guy? What's your strategy for taking him down? I'm playing on PC with a keyboard and mouse, if that makes a difference. I feel like I'm missing something obvious, but at this point, I'm willing to try anything.