Wider vent, redder comb. Open up the nesting boxes at 14 weeks so the hens get used to them. For my first hens I didn't put fake eggs in the boxes, the hens just knew where to lay but I would put in the fake eggs at 15 weeks.
Reddening combs, squatting when I approached and put out my hand. Not all hens will squat but I actively encourage it so so far all of mine do, and will start laying 7-14 days after onset of squatting.
I'd open up nests once you start seeing noticeably redder combs, to give them some time to explore the boxes before they need to use them.