Hi,
In onepage checkout you can add one feature (in obile it's most important). When we fill all field but miss one from required. We should have two actions to support Client.
If client miss somethin...
1. Near next button you should show error/monit, something like *you must fill all field.
2. Move Client to first missed place.
Now we show only informations below field, but Client don't know, why next button do nothing. We have two scenerio, he start scrolling and see error, or he abbandon cart.
I think it's good way to help Client in this most important place, and help him.
Best wishes!