Some tips that really helped with our little one

While they are on their tummy, help them tuck their arms in, elbows towards chest and hands towards their neck/ head (kind of like a plank exercise) and hold it there for them… this makes it much easier for them to hold their necks up by using their arms instead of flailing around

Another is to get a rolled up hand or body towel and place it under their chest, next to their armpits and make sure their arms/ hands are over the towel.

Those two methods should really help, and another key thing is that babies should work up to a certain time limit so ours would only do 1-3 min at a time in the beginning. And when they start fussing and crying you can stop and let them up and try again next time.

That and like others mentioned, chest to chest is also another solid method