1. If your baby likes to straighten his/her legs while you are wrapping, you can put one hand back to hold baby's legs in position until you are able to remove slack from the tails and create your next pass. Also, babies that like to leg straighten will usually stop if you stand up a little (while keeping a hand back to hold their legs in position).
2. If you find that you have a great seat, but you are losing it after you tighten your carry, you might be over-tightening the bottom rail. Seats are kind of picky about how much you tighten them. If you tighten too much, the bottom rail will tend to creep upward, slowly causing your seat to get shallower and shallower. This can also cause red marks behind baby's knees or thighs. When you are taking slack out of your passes, don't aggressively tighten. Just feel for excess slack and remove it.