Bug spray, and lots of it, is always a good idea. Chiggers and dewberries go hand in hand. Dewberries look like tight red raspberries before they ripen. Pass those over and go for the dark, purple-black ones. You'll find that the plump ones are usually the sweetest.
Tasting is mandatory.
Just make sure you don't taste too many. The goal is to bring enough home to make a dewberry cobbler or two. My husband was raised in San Antonio, where weather conditions and the scarcity of wide-open fields thwarted his exposure to dewberries. Lucky for him, he met me seven years ago and I introduced him to the joys of berry-picking. It's no coincidence that we married just over a year later.