Is there any particular place on the crown molding where I should position a nail (middle, inside creases, top, bottom, multiple locations)?
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.
I always put the nail on a part that is accessible by sandpaper and a finger. Otherwise it will be hard to fill and sand.
Gents using a triangular backer is a great idea but unnecessary... It is a very light molding per foot, simply tacking it to the sheetrock is more than adequate. By the by, due to thermal expansion issues, even in newer homes that have not settled it is a mistake to nail your modeling to the ceiling. Most of these crown moldings are only intended to be nailed to the wall (yes there are profile exceptions) check your profile. If it has a single broad flat area where it contacts the wall, that is where it should be nailed only! I've seen numerous homes where someone nailed to the ceiling and wall and it pulled on the wall or ceiling and caused cracking. If you do the backers you won't need to worry about those issues, your project just takes much longer especially if your are measuring the actual angle that your wall/s and ceiling make where they meet in the corner. Rarely do I see corners that are within an eighth of an inch. As far as a smooth finish goes for nail holes, use paint able caulk, then dip your finger(or caulk finishing profile) in water and run it over the spot. Nice, smooth, perfection!!! That's the way to finish without sanding!