In the beginning for us, I went by fussing/squirming as well as timing. Also, I put LO on the potty with every diaper change. I recommend getting a top hat potty. The times I forgot to put her on the potty at diaper changes she would get so mad and remind me. Our misses were usually just "warning pees" and she would finish the pee at the diaper change pottytunity. It was a while before we got any good at catching poos because my LO had food intolerances and basically was fecally incontinent. Once I got the food issues under control she led the way by saving her poos for a pottytunity.
I got Diaper Free Baby but wasn't a fan. I would suggest any other book, personally.