In general:
Pick fruit that is heavy for its size. That means it is juicy.
Watermelon:
Look for sting marks…means it is sweet. Thumping should give you a hollow sound.
Pineapple:
Look for a short stem…means the “growing effort” and therefore taste went into the pineapple. Look for a yellow color in the skin. Means it is ripe. Smell the outside. Should smell sweet. (If the scent is overpowering, it might be too ripe.) Pineapples don’t ripen once picked, so choose one that seems perfectly ripe. They soften and lighten in color once picked, but they don’t ripen.
Cantaloupe:
Squeeze it. Should give a little. Hard=not ripe. Squishy=no good. Smell it right where it was removed from the vine. Should smell sweet. Look for a golden color. (If it is green, it will ripen at room temperature within a few days.)
Peaches/Nectarines/Plums/Pears:
To speed up ripening process, place fruit in a brown paper bag at room temperature for a couple of days.
Strawberries:
Look for plump, bright red, ripe berries. Look for green, fresh-looking leaves.
Other berries:
Avoid containers containing juice stains. It means the berries were squished and possibly moldy. Wrinkled fruit = old fruit. Plump fruit = fresh fruit.