Practice, practice, practice......then practice a little more.
It takes "time" to develop the "feel" for what you're wanting to do. I did it years ago and got away from the practice. I lost my "touch". But, with 38 does being bred on a 17 day breed back, I'm having to learn the method once again.
Start at 14 days...and work your way "backwards" to 10 days once you become confident with your method. I always palpate the doe in her pen. She's more relaxed and her muscles are less tense. It takes a certain amount of pressure with your fingers gently closing together and slightly moving your hand forwards to their mid-stomach to feel the babies in their stomach's towards the back-end of their torso. They're sort of like small "squishy" grapes slipping through your fingers when you slowly move your hand forwards.
I've become more confident with my practice and now only miss one or two out of 15 or 20 does. Again, it's a learning-experience that takes a great deal of practice. Also, I've got a commercial herd of NZW's. Those commercial does are long and lean which makes it easy to palpate them. I rely on my bucks to put the width on the fryers.
grumpy.