I pass it through the top centering ring and knot it around the motor mount, like UhClem said, for smaller birds. On my larger ones, I take it through the top CR, fray it out, and wet it out with Aeropoxy. Then I wrap it with a layer of 9 oz. glass.
If I have the room, though, I like to attach a u-bolt to the top centering ring and attach the TK to a quick link and then the quick link to the u-bolt. This makes it easier to replace the shock cord if (when) it wears out. I tie all my TK and TN with double figure eights or figure eight follow throughs, as one does in climbing. If it's strong enough to hold me when I fall off a rock, it's strong enough for my rocket!
I think the best way to INSURE a solid hold is to get a plugged forward closure, drill and tap for a forged eye bolt to be in it.(assuming your not gona use motor deployment) Sew a loop on the end with at least 8X the diameter of the kevalar overlaping itself, atach it to the eyebolt with a quicklink, and make sure your end closures are on VERY tight so they don't unscrew themselves as the rocket is spinning on its way down. I know this is over-kill but I've seen many separations becasue of poor anchors to the rocket body.
In my case, I just glue the end of the kevlar to the inside of the coupler that joins the forward airframe to the tail section. I use thick CA to glue it. This coupler is removable, held in place with small screws.
If you want a loop, just double it over and knot it to make a loop to attach with a quick link, as Ryan suggested.
I read this thread and had an idea. For those of you that might be just epoxy the TK to the inside wall of the tube, consider this. Before you attach the TK, trim a small rectangular piece out of the tube, but don't go all the way through. Then lay the TK down in that hole, and slather the epoxy over it. My thinking is that this would allow the epoxy to soak through the TK and the inside layers of the body tube, creating a stronger hold.
Then, of course, you could always use a eye bolt in a centering ring or something like that...