Time and patience. The key is not to do something that scares them, you just have to get to know their body language.
Persistence helps,spend lots of time socializing and sort of let them do their thing their way.
Some sit in a bathtub with them, a bag of treats, and just let them have at it. Never force them against their will.
If they choose to avoid you, give them that freedom of choice, Trust is learning hands won't hurt them won't grab them or chase them. They need to see your hands are something good. As you note, they have individual personalities.
Some nearly come tame, others may take weeks or even months. when they feel frightened, they need a place they can hide and feel safe. This may show a hamster, but much the nature of any small prey animal.
https://www.youtube.com/watch?v=2g0X7Nje9PI
Much like this has worked across the board for me, even some wild critters like fence lizards trusting to nearly take meal worms from my hand although it did take months and persistence and lots of patience.
Some videos I am sure will help, Rats are very smart and do learn faster than some other small animals.
https://www.youtube.com/results?search_query=how+to+tame+scared+rats
None of my ratties seemed to favor being picked up but with trust, had no problem tolerating lifting and of course freely climbing onto laps for treats
Hope this helps speed things along.