avocados:

Picking:  If ripening a day or two before, you can pick a lighter green one, which will feel like a rock and not squeezable, and put it in a paper bag with an apple to ripen it.  I often just leave it on the counter and wait for the color to change; avocados ripen quickly.

An avocado that is a darker green is usually ripe, but if the skin feels a little too soft, like the skin is loose or shriveled, chances are you've found an over-ripened, bruised avocado, which isn't so great.  The best avocado is one that is slightly squeezable, and a darker green without being almost blackish-green.

Seasons (from ehow):  Haas avocados are available year-round but are at their peak from April to November. Fuerte are available from November to July. Reed are available from March to September. Booth, Lula and Taylor are available from the end of June through February. Zutano are available from October to May.  Bacon are available from November through July.

Here's a simple video for how to prepare avocados.  I use the same methods--cut in half, twist, chop knife into pit and twist to remove, use a butter knife to cut through, and scoop out with a spoon.