Some snakes are easier than others. Over the years I have acquired several already mature snakes that had been fed live, and some will just switch over without any hesitation whatsoever. Some take a lot of patience, and that is the biggest thing. If they refuse a meal, don't offer again too soon. If it's a mature adult, I would wait 2-3 weeks before offering again.
Technique is something really helpful for some animals and over the years this is what I have learned:
-The head is naturally the hottest part of a live animal so taking the fully thawed and just warm prey and zapping just the head with hot water or a hairdryer for a couple seconds immediately before offering helps.
-You want to grip the prey with the tongs at an angle where you can maintain it's natural shape and stance to look as close to live as possible. About a 20 degree angle compared to the animal will help it hold up more horizontally, and I find grabbing about 1/3 away from the butt is the best place to grab.
-You are most likely to get a strike as the prey passes the snake walking past it, not towards it.
-Mimic the natural movement as much as possible by jiggling quickly for a split second and then pausing for a few seconds, alternating.
I've never had to resort to trying live again for an adult animal with these techniques. Sometimes for hatchlings, it's a must because they just can't afford to loose much weight and you have a smaller window to work with, but even that is really rare for me.