I have a piece of inner tube about 1" x 3" that I keep clipped on my fishing vest just for that purpose. Works like a champ.A piece of rubber, like from a tire repair patch set works well at straightening out curls in leaders.
Put the leader in the rubber, fold over and pull the rubber down the length of the curled section.
This...Don't put the fly in the hook keeper. Make sure the entire leader is outside the rod tip, then bring the leader around the reel foot and hook the fly in one of the guides farther up the rod.