Put on an apron or outfit you don't care about staining.
Cut the fruit into quarters, or score the skin in quarters, then pull the fruit apart.
Working over a large, deep bowl, gently loosen the seeds with your fingers. Discard the pith and skin.
You can also remove the seeds with the fruit completely submerged in a bowl of water. The pith will float to the top; the seeds will sink. Scoop out and discard the pith, then drain the seeds in a colander. While this technique is less messy, you'll lose a bit more of the fruit's precious juices.