Also make sure nests are easy to get in/up to and out/down from.
More info needed:
New layers?
Older birds bullying pullets from nests?
Not enough nests to go around?
I've had a couple pullets that did not like the fake eggs at first.
When I have new layers in the coop I always leave one nest empty of fakes.
Always a stubborn(or stupidish) pullet that lays elsewhere than nests.
Finally caught one the other day after a half dozen eggs on floor, I watched her lay on floor then grabbed her in her post laying stupor and put her in a nest. She did not like it. Next day saw her settling into same place on floor, shooed her out of there and put a bucket in that spot. She finally got into regular nest and laid, we will see if it 'takes' long term.