It really depends on the situation you're in.
Here's 3 examples of possible situations:
1. In water
2. On flat land
3. On a mountain
Water: Blockhit. That's the best way to avoid taking damage. If you can do it right, then it's possible to outlast an opponent with much better gear (Although if its full leather stone sword vs iron armor, diamond sword, just run away.)
On flat land: Strafe! Get behind the opponent. Blockhitting can be easily defeated if you are a good strafer - I speak from experience. If the other person can't hit you, then you don't have to blockhit. Run around them, but don't take wildly large loops around them. Make small circles, not large ones. That way you move around the opponent faster and they have less time to react. It's tough to do this right if you're using a trackpad, unless you're really good with it.
On a mountain: Get above them, if you can. Then you can sprint at them, using the knockback to hit them off the mountain. Deals a lot of damage, has the chance of a critical hit, and they will fall, hurting them even more. If you can't sprint, though, due to either lack of space or just bad sprinting skills, then blockhit. They can't strafe around you easily (Unless they hack and/or are really good), so if you blockhit then you will hopefully be able to outlast them, just like in water.
Hope this helps you.
Oh, another thing I wanted to write:
Flint N' Steel and Bows.
Flint N' Steel will stun their sprint and deal tons of damage. As long as you can avoid lighting yourself on fire, it is very effective unless they dodge it. Don't use it when they are far away, as they will just avoid/extinguish it.
Bows: Long-ranged weapons. When fully charged, they do as much as a diamond sword (I think). Great for hitting people off mountains, pushing them away from you in water, or hitting people who are in water. Assuming you have decent aim. It helps, as well, in DeathMatch - Aim at them, then fire once you are free to move around. A good way to stun their sprint and/or get the first hit.
lol
