THIS right here is the secret, I put all of them on, (which takes about 10-15 seconds) then immediately go to the first one and turn them over, once you see the smoke , you are safe, it is not going to come off.
However as Oghab said, you also need to get the mixture right. My go to is 1-3 Lamb-beef , for best result, let the goosht "BAYAAT" it DOES make a difference, however if you are short on time, TINY TINY TINY bit of "Jooshe Shirin" does the trick, be very careful though, if you do this too much, your Kabab is going to be like "LAASTIK!"
I was watching some restaurants in Tehran, they WARM the mixture (ground meat) before adding onion to it, I have never tried this, but maybe I do this weekend!