Dry Fitting.

Dry fit the moulding in the room. Use low tack tape to hold it in position if the house can’t be turned over. If everything looks good remove the moulding to paint.

When the paint is dry glue in. After the glue is dry, check to see if any of the corners need to be touched up. If they do, protect the ceiling and walls with painters tape and paint. It is easier to fill gaps with paint in minis than with wood filler.