To evaluate a hand when they first see it, most players count their points.
The 4-3-2-1 scale originated almost a century ago and is widely used still. Other scales, which claim to more accurately reflect the trick-taking power of the honors, appear from time to time. The Robertson 7-5-3-2-1 scale and the unwieldy 13-9-5-2 scale may be better in theory but lack the virtue of simplicity.
Good players know the shortcomings of the 4-3-2-1 count: Aces and kings are undervalued, queens and jacks are overvalued. A hand such as A K 8 7, 6 5 4, A J 8 7, 8 7 is worth opening because the values are prime and the jack of diamonds is more likely to win a trick when the ace supports it. But few players would open with Q J 2, K J 5, Q J 4 3, Q 6 5.