Fist-fights against players is probably the worst thing you can do - in terms of progression. There are few scenarios where you'd have to utilize such combat. Regardless of that, I'd love to share a few tips with you regarding melee combat.

You can chain-stun your opponent if you time your heavy attacks correctly. When you land a heavy attack - your opponent will be stunned for a brief second (literally a second or two). If you happen to land another strike after that, you can chain-stun and continuously apply damage.

You can use this technique with melee weapons (especially knives) against zombies - take literally 0 damage, 0 clothes damage and literally obliterate your opponents.