The raglan seam itself can be as simple or as complicated as one likes. It can be as simple as a single knit stitch or as elaborate as a cable pattern (p2cable4p2) -- as I saw on an episode of Buffy, the Vampire Slayer -- or a k1p2k1 pattern as in some of the sweaters I've posted directions for.
I like to be able to easily match up patterns on the sleeve with patterns on the front of a sweater, and I've also discovered a way to keep there from being holes near the bottom of the armhole -- which involves hiding 1 or 2 stitches from the raglan seam. For a raglan seam with an odd number of stitches (as in the boat-neck sweater pattern in this blog), allocate the central stitch to the sleeves. For a raglan seam with an even number of stitches(as in the ribbed sweater with turtleneck option pattern in this blog), allocate the central two stitches to the sleeves, and then just before the underarm seam k or p tog to give a single central stitch. The central stitch will disappear when the sleeve is added.
Increases are made on both sides of the seam (paired increases). In general, increase on every odd row until 3 rounds of increases are left. Increase every fourth row after that. Finally, knit without increasing until reaching desired number of "rows above underarm seam".
To match designs on the sleeve and garment body, keep this in mind. With S the number of sleeve stitches at the neck and B the back and x the extra raglan stitches belonging to the sleeve (2 or 4), if two sleeve stitches have z stitches between them, the corresponding front (or back) stitches have z + B – S + x stitches between them.