Stinging nettles need to be harvested while they are still young. Anything taller than your knee is too tall and the stalks will be woody and tough. It's better to cut them rather than pinch or pull them up, and always leave several leaves on the plant so it can continue growing.
I guess most people use rubber gloves to handle nettles in the kitchen, but I used my favorite cooking hashi (very long chopsticks). Rinsed them well in cool water, then blanched the nettles for 30 seconds to remove the "sting".