Where should I place nails when installing crown molding?
What is important when nailing crown molding is hitting a solid background. This can be plates for small crowns or studs. What I prefer to do is add a profile (triangle) piece of scrap wood, such as mitered plywood or ripped 2X4 stock into the corner and nail it into the plates and studs. No problem if you miss or have to use a lot of nails to find a good solid backer because it will be covered by the crown.  Now when you go to nail the crown, you will have a good nailer everywhere.  I usually use nails along the top edge down 1/2 inch from edge and same along the bottom edge.  This helps close any gaps along the ceiling and wall. You can go back after and fill any gaps with painters caulk and touch up to match the crown (if painted) or the wall/ceiling colors respectively.