I've had two really good invasions.
The first one went like this. I had the Fog Ring on and was standing out in the forest part, by where the Cleric usually is, and there was the host and a white phantom standing by the staircase. They had no idea where I was, and so I watched them for about 30 seconds. I took out my bow and shot a teasing arrow at the white phantom right when another invader came in. The White Phantom ran off to engage the other invader while the Host stood off to the side with his shield up. Right when the WP got far enough away, I rushed the host and backstabbed him, which didn't kill him. But he was so freaked out that he tried to roll away and... went right off a cliff.
The second time went like this. I invaded a guy, and right then a red phantom invader came in. I charged up behind the red phantom as he battle the host, unseen, and took him out in a single hit (this is MY forest, these are MY kills). At this time, the host ran up the stairs and shielded up and I ran into the forest. He was a short range magic user and I use my sword, so as long as we stayed 40ish feet apart neither could do a thing to each other. So we toyed back and forth for a little bit when another invader came in. I backed up and pretended to be hiding when the other invader came up, and then goaded him into attacking the host. The other invader got demolished and I bowed to the host once more. Finally I charged him after waiting for so long, got in a few hits, but ultimately lost. Ah well.
Still, it's a lot of fun.