Normally, you stitch the Tent Stitch with all the diagonals in the same direction. However, a different effect can be achieved by alternating the direction of each stitch on purpose.

The first pass of stitches in this pattern is the regular Tent Stitch, but only every other row. Stitch the opposite diagonals in a second pass.
First Pass:

Second Pass:
This pattern, among other things, is especially good for plaid designs.

Another interesting way of alternating the Continental Stitches is to switch the diagonal on every row instead of every stitch. This gives the pattern the effect of horizontal ridges.