When knitting cardigans, you are making two fronts that are reversed and mirror images of each other. The armholes are on opposite sides of your knitting as is the neck shaping.
The neck and armhole edges are at their logical, respective places. When you are knitting the right side of the piece, you are looking at the reverse of how it will be worn. With the right side of the work facing the public, hold the left or right front up against you. This is the easiest way to tell which is the armhole edge and which is the neck edge if you get confused.
Almost all cardigan patterns will give you exact instructions for knitting one front; the instructions for the other front will usually tell you to knit it the same way, but reverse shaping. This can seem like a cryptic instruction intended to confuse you, but it avoids pattern errors (like one side being written one way and then the other side being written differently).
To reverse the shaping, work the shaping at the opposite end from where you worked it for the first front. The armhole shaping and decreases must be at opposite ends so that when it's sewn together, you will have one armhole on the left and one on the right. The neck shaping must be on the inside of both pieces, where it would logically be.
Usually you will begin to shape an armhole by binding off stitches. If you bound off the stitches at the beginning of a right side row for one front, you would bind off stitches at the beginning of a wrong side row for the other front. You are always essentially reversing the right side and the wrong side rows. This keeps the shaping on the correct edge (for instance, the left edge versus the right edge). Remember you can only bind off stitches at the beginning of a row and have the yarn be in the correct place to continue across the row; thus, you will be one row off numerically (you may be binding off on row 25 instead of row 24), but this will not effect the end result or the look of the cardigan.
If you are increasing or decreasing at the beginning of a row for one front, you would increase or decrease at the end of the row for the other front.
And again, remember if you get confused just hold the piece up against you as if you were wearing it to tell which side is which.
For more articles from Barbara Breiter from Understanding Common Pattern Terms to Using Color Changing Yarn, click here.