When I started to fingerpick I used to use my thumb (or thumbpick) a bit like a flatpick, doing a lot of the melody work. I came across an interview with Ralph McTell where he said you should confine your (right-hand) fingers as much as possible to specific strings. So, the thumb stays with the 6th 5th and 4th, first finger plays third string, 2nd finger plays 2nd and third (ring) finger plays 1st string. This is probably well-known but I wasn't really conscious of it before and it steered me in the right direction. Maybe I didn't explain that very well, but it was a great help to me, and now I can finger-pick just fine! It's worth a bit of effort, so much more enjoyable than flatpicking when you get into it.