This Old House has an article on it.
Installing crown molding, however, is a task that strikes fear in the heart of every amateur carpenter \ufffd and even some pros. Because it sits at an angle on the wall, each joint is made of compound angles. Getting it right requires a lot of patience, an aptitude for spatial relations, and a few tricks from an experienced pro.
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He [Tom Sliva] also doesn't lay the molding flat to cut it. Cutting crown flat, though it might seem easier, requires a saw that lets you tilt the blade (for the bevel) and rotate it (for the miter angle). You also need a set of tables to know the correct angles for the cuts.
Instead, Tom uses a simple power miter saw and arranges the material so it sits against the saw fence at the same angle it will be nailed to the wall. Although the molding has to be upside down in this method, a simple downward cut of the blade set at 45 degrees produces the perfect miter and bevel at once, as you'll see.
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Inside corners are composed of a square-cut piece that butts the corner, and a corresponding piece that\ufffds cut on an angle and coped (carefully cut along the molding\ufffds profile) to conform to the first piece.
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* Highlight the very edge of the cut, along the profiled front of the molding, with a pencil.
* Next, using a coping saw, cut away the bevel. Angle the coping saw blade toward the rear about 5 degrees \ufffd a technique known as back beveling \ufffd and carefully follow the molding profile as you cut (above). Use the miter saw table to brace the workpiece when cutting.
It's not for the faint-of-heart. There are types of crown molding that don't require complicated cuts, they use various box elements to ease some of the installation to eliminate the coping, etc. Lowes and Home Depot carry the things. But they're not cheap either.
HTH a bit.
Cheers,
Scott.