First up and easiest is take out the ones with a hairy tail. Those are males.
If you pick an adult male up, you will feel in your hand he's raspy and rough.
I found out recently if they have yellow spots around the vent area they always seem to female but not all females have it all the time.
Males tend to just look sharp and girls more curvy and rounded. It can very subtle and juvi males will at first tend to look more female.
Theres heaps of stuff to look for but very few traits on its own will definitely point to one sex, its a few things together and even then you can get it wrong.