BIG HINT: the produce guys at any good store will walk you through finding the best and how to.
It's different with every category of fruit/ veggie/ root/ herb/ melon
A few things I DON'T see people doing (buy should)
- bouncing oranges - aka hand weighing, although a scale works hand weighing is faster (heavy ones have a lot of juice, because they were picked later, so are sweeter and more 'orange' tasting.
- squeezing garlic heads (they should be rock hard, a soft head means its either growing or breaking down into dust)
- peeking in artichoke leaves (avoid the thorns, but mealworms love artichokes. Any black dots inside the leaf pack means worm poop, which means a worm about half the time)
- thumping melons... All melons should sound hollow. Drum on a bunch lightly with straight hands, and you'll hear the sound difference.
- smelling tomatoes. Tomatoes should smell like tomatoes. If the don't, they're just red things with no flavor.
- checking mushroom gills in button mushrooms... Those mushrooms should have sealed gills... And be eye popping white or very dry brown tops (wash both VERY well, they grow in maneure)
- feeling up pea pods. If you can't feel the peas in then they fonts have peas yet and were picked too early.