There are so many rumors about eggplant, and almost none of them are true.
You'll find even knowledgeable cooks telling you that you need to select female eggplants because the males are bitter. They'll tell you to check whether the flower end is pointy or ridged. Some will say that if they have large green caps, they'll be more bitter. Or that heavier eggplants will be more bitter.
And they'll tell you that eggplant always needs to be thoroughly salted before cooking.
Let's deal with the bitterness question first: No. Aside from some Southeast Asian eggplants that are prized for that quality, it's age that makes eggplant bitter.
As for salting, the "no" is more conditional: If you're going to roast eggplant or steam it or grill it, salting makes no difference at all. But it will make a big improvement if you're frying the eggplant, though the procedure is a little more involved than a quick sprinkle and rinse.
Salting eggplant before frying draws out extra moisture and after frying the flesh is incredibly plush and creamy. But the eggplant needs to be thoroughly salted: Cut it into cubes or slices, salt it liberally on both sides and arrange it in a colander with some kind of weight to press it. Leave it for at least an hour – preferably 90 minutes – and rinse and pat it dry before frying.
How to choose: Look for eggplants that are firm, even hard to the touch. They should feel as though they're almost bursting from the skin. There should be no shriveling or soft spots. Also check the calyx (the green leaves at the stem end); it should be fresh and green, not dried out and brown.
How to store: Oddly enough, eggplants are tropical fruits. It's best to store them at room temperature, at least for a day or so. After that you'll have to refrigerate them before they get too soft, but you don't want to do it for too long, because they suffer chill damage fairly quickly, creating soft spots.