There are many and i mean MANY ways to PvP, and i just dont have the time to go over them all. So, i will be going over the 3 most basic (and important ways) to Pvp correctly.
1- Have you been running straight into your opponent? You should never do this becuase if the person your fighting has better gear than you, you may find your self at the re-spawn screen! To fight your opponent the right way, you have to strafe! Strafing is where you move around your opponent while hitting him. This will make it hard for your opponent to hit you while you remain in control! Strafing can be zig zag circle etc.
2- Critical hits! Hitting a player while falling will do a whopping 50% more damage then hittingg him level! You do this by spamming your jump button while hitting your opponent! This tactic is best used when your cornered or in a narrow place where you cant strafe.
3- Use tools other than your sword or axe! You other primary weapons are: bow, fishing rod, water, lava, and eggs or snowballs. You can use these in many different ways, (but of coarse it would take forever to write so i will tell you one thing: switching back and forth from sword to the tools i just mentioned can confuse and stress your opponent witch will give you the advantage! These are the 3 basic PvP tactics! (in my opinion) Try em out and have fun!