distraction can help
When our snakes were very young we found that distracting them with things to smell helped a lot when getting them used to being handled. My daughter and I used to let our snakes smell book shelves, toys, windows etc. It distracts them from being held so you can handle them for a longer period of time.
One of our snakes who's almost a year old now still doesn't want to be handled at times. I can always tell when it's unhappy because it shakes its head back and forth in sideways bobbing type motion as if to say no, no, not today cowboy. If I want I can still handle him, but it just stresses him out so I usually put him back in his viv after a short hello.