OK, mamas, I consider myself to be highly uncoordinated with slings (I never got the hang of my Maya, and I feel like such a loser!), but even I can get a wrap to be comfortable. DON'T GIVE UP!
First of all, I wouldn't attempt to do the back carry as a "first position." I'd do the wrap cross front carry
to start with. Practice WITHOUT your DC several times so that you can get comfortable with the idea of the wrap. I also recommend what Tupelo suggested, which is to fold the fabric in half width-wise (the short way). . .it's much easier to work with that way.
Three words to live by: high, tight, and smooth. Start as high as you can. For example, when you bring the fabric around your waist for the wrap cross carry (the very first step) put it really high . . .much higher than what the model is demonstrating on Peppermint (esp. if your fabric is folded in half). As you're doing each step, smooth and tighten the fabric.
I do find that the wrap isn't something I'm going to use for a short walk, and I'm not yet comfortable doing the back carry out of the house. I still need to concentrate when I'm tying, and I'd find it too distracting to be out of the house to do this. I can handle doing the carry I mentioned above while out, but I tie it on before I leave the house.
Oh, and I'm considering sewing a little thread in the middle of my wrap as a marker . . .I do get frustrated finding the middle sometimes!