Grip loosely, don't clamp

The most common reason for tired, aching hands isn't lack of strength but too much pressure. Beginners clamp the strings as if they had to push them through. All that's needed is enough pressure for the note to sound cleanly — more tires the hand and tenses the forearm. Check consciously now and then: does it work with less? Almost always yes. Tension is a technique signal, not a strength deficit — and it goes away with cleanliness, not with muscle training.