Probably not the answer you are looking for but to me, there is no one or two or ten "most important" things to BW - there is only what are the most important things to you and your baby. For me, rocking/cuddling/snuggling to sleep was important - I felt my baby needed it, wanted it, enjoyed it, and so did I. He thrived in the comfort and closeness of sleeping next to me - and didn't wake up when I put him down, and didn't wake in the night needing cuddles to go back to sleep, so I didn't mind it at all. Yet I know there are other BWers who feel the opposite (probably most in fact) and their LOs have different needs.
For me personally it was treating my baby as a human, a person with feelings and needs, and someone to be spoken to not over. ie/ I would rather have argued with my MIL about insisting she refer to my son by HIS NAME rather than calling him "the baby"; I insisted he not be taken and passed around like an object to gawk at but that it be recognised he would rather just sit in his bouncy seat and watch everyone at the moment, etc. I insisted that when he was tired he was allowed to sleep rather than "oh but auntie so and so will be here in 20 minutes and she would love a little cuddle..." - those things moreso than x amount of A time, etc.
What about getting your copy of BW and going through and highlighting or marking the things that mean a lot to you and asking your mother to read it and then talk about them with her just to explain to her why those things mean so much to you, what it means in practice of day to day life and see what she thinks and feels about them and chat through them to see what things you are on the same page with and what things you will have to work on?
