The most important thing is that your snake eat SOMETHING. If it's refusing FT, don't let it starve to death--give it live.
Once it's had a few meals, work with it--offer it food and leave the cage open while it strikes its prey. Then offer it pre-killed prey on tongs. Then frozen/thawed prey that has been rubbed into fresh mouse pee (this works like a charm for me). It usually only takes 1 or 2 feedings like the last one for the snake to accept frozen-thawed mice that aren't scented.
Once it's eating FT, you shouldn't ever have to go back.

Not all snakes will convert to FT. I have some that are too shy to eat with the cage/bin open. I have some that will take pre-killed off of tongs, but come up all excited, take a few 'sniff's, and then give me the DIRTIEST look when I offer them scented FT, and turn around and move to the back of the bin. <lol>