I read the book Natural Infant Hygiene and did it with #3dd and #4dd. I started right from birth. It was amazing compared to dd#2 who had diaper rash from all the cloth diapers and disposable, I wish I had known about it earlier. She is the only one who still pee's the bed and she's the oldest. The earlier you start the better in my opinion. My other two rarely if ever peed the bed starting from 1 month old, unless I was too lazy to get up to take them. I had a bowl by the side of the bed made it easier.
I love elimination communication and it seems like the babies love it too. I help my neighbors with her two babies 15mo and 4mo and they NEVER have to experience a dirty diaper, poop on the but. They always wait until someone takes them, except the 4mo who will poop if someone doesn't take her with in a few (10-15 min at the most) minutes of her needing to go. Peeing they seem to have less ability to hold it but I've seen her and my dd hold it for up to 5-10 minutes, starting from 1 month old.
It's all about body language, sounds, and cues. She squirms or gets still when she needs to go depending on what she's doing. Usually if she's already squirmy and playful and then is still or if she's already still then she gets squirmy and the cry is a little different from other types of crying. It just takes paying attention, close attention.
Also intuition. Sometimes I just think, she needs to go and I take her and she goes.