Go out for a ride and find your comfortable spot on the saddle. Once there, hold your left or right foot down at the bottom of the stroke as you would while pedaling. This is assuming your cleat position accounts for any discrepancy in leg length.

When your foots at the bottom of the stroke in your normal pedaling motion, push down with the foot that you have at the bottom of the stroke. If your butt rises off the saddle, your saddle's too low. If you can't apply pressure to the pedal at the bottom of the stroke, your saddle's too low and you'll probably have trouble with hard corners.