I think it's a trial and error process, unfortunately.
I've learned which juices need steeping, and which don't.
I think there are some pretty basic rules to steeping:
1) Store it in a cool, dark area.
2) Shake it vigorously any chance you can get.
3) Take off the caps and leave them exposed to air overnight (to evaporate alcohol). How many nights is up to you. There is no set in stone rule.
4) Look for color change.
5) Shake vigorously!
6) It's up to you at this point to decide if it's ready or not to
vape.
(edit: holy crap, my numbers are off!!!! So much for posting on my days off.... Editing the list so the numbers are correct... /embarrassed)
In regards to rule 6, I have to suggest something I heard on here as advice: "Vape it. If you don't like it, let it steep some more. Then try again."