Dark nest boxes helps in many cases. If you have a roo, make sure you show the roo the nest box---the roo will suggest to the hen where to lay eggs--and roos typically choose places that are dark and cozy!!!! It's fun to watch him cluck and coo to show a hen where he wants them to lay!
The use of golfballs (over other "fake eggs") has multiple advantages....it lets the girls know Where you want them to lay- as well as if they get pecked at they get their brains jiggled---yup--it's why it works better than other fake eggs for egg eaters. It works as an instantaneous negative feedback
Extra protein is also helpful. Many chickens will go after the eggs because they are starved for protein. Be careful using too much catfood--as it has more selenium than you want to give to birds (they need micro amounts...but too much can kill them of cause birth defects)...it's great as a short term solution, but it should be just that- short term. Other protein treats can be worms dug up from your garden, meal worms from the bait or pet shop, your meat leftovers from dinner etc.
Calcium can be a problem also. Many folks who give layer feed don't give additional oyster shell free choice because there are oyster shells in the feed. Chickens need more calcium sometimes than others...only by giving them extra oyster shell at all times for them to eat when they need it will this be rectified. ALso, if the shells are soft...the eggs may crack and once it's cracked, I know of NO chicken that won't eat what is there!!!----which goes to what mystery chicken said "one cracked egg in the corner of the shed. NOT cracked by a chicken but by the fall off of the grain bag that someone keeps trying to lay eggs on."....I don't know of any chicken that wouldn't eat that egg and then go back there to look for more later!!!!
The rollaway nest box can also be very helpful...but for me it's too much to build it---a simple box is so much easier and less time consuming!
Good Luck ALL
Sandra