ditto what speckla said...
Search youtube for "transitioning hair braid out" or "transitioning hair bantu knot out" Bantu knot outs are curlier, but will still blend your roots well. I was going to link one, but there were too many good tutorials for me to choose from lol
But you just would want to use whatever leave-in you like for moisture and something with hold. If you hair likes oils, a pomade would be good for that (sealing in your leave-in and styling).
a few tips I picked up is:
1. don't do the cornrows straight back, they sometimes fall awkwardly. Braid so they will fall in a way that frames your face.
2. Braiding the ends of the cornrows (your loose hair) with a satin scarf makes the end smoother (but it's not really necessary)
3. If your ends have a hard time curling up, put a perm rod or some other kind of curler on the ends so it will blend well