If you find that eggplant dishes often taste bitter, try this trick.
If making moussaka or eggplant parmesan, cut the eggplant into slices for use. Sprinkle salt over the eggplant slices on both sides and let sit for about 10 minutes. The salt will make them sweat their bitter liquid out. Wipe this off with a (paper) towel and your eggplant dish will not have that bitter flavour!