Apricots. Look for plump, firm apricots with a pretty red blush. Avoid fruit that is pale yellow or green-yellow, very firm, very soft, or bruised. Availability: late May to mid-August.
Blueberries, Strawberries, Raspberries, Blackberries. Look for blueberries with a rounded shape and a tiny star-shaped cap. They should be firm, plump, and sweet. Strawberries should be plump with bright green caps and a healthy red color. Size does not indicate quality; the largest strawberries aren't necessarily the most flavorful. Raspberries grow in various shades of yellow, red, and black, and contain many tiny, edible seeds. Blackberries should have an inviting color ranging from purplish black to black. Beware of excess juices in the bottom of the containers -- this is a sign of spoilage. Sniff for mold too. Availability: all summer long, depending on the region.
Melons. Pick a juicy, heavyweight contender. Cantaloupe should have tightly-netted skin; honeydews should be smooth and unblemished. Poke and whiff the belly-button, or blossom, end; it should give a little and smell melony. Melons will soften but not sweeten further when left to sit at room temperature. Availability: nearly year-round.
Peaches and Nectarines. Watch out for greenish ones; they won't ripen. A rosy blush is nice, but not an indicator of ripeness. Use finger pressure; ripe peaches feel slightly soft, yielding. Ditto on nectarines. Availability: peak from June through September.
Plums. A plump shape, vibrant color, smooth skin, and moderately yielding flesh are good signs. Stay away from soft, leaky ones. The bloom (light gray cast) on the skin is natural and doesn't affect quality. Avoid exceptionally hard or soft fruits. Availability: June through September.