1. Practice makes perfect. This is how you get better at PvP. Also watch some tutorials on how to PvP better (fishing rod tecnique, block hitting, etc). When Optifine comes out, download that, as max performance is a must for PvP. If you have the money, upgrade your mouse/keyboard if necessary to allow for more attacks and better gameplay. You can also be tactical with it, and attack them into a corner so they can't run, or attack them while they're opening a chest. Fire is also a great tool - use it! Plus bows are helpful to get people on low health while they're running and for deathmatch.
2. Don't hit land. It slows you down greatly. Try to make smooth jumps, and if you can, run them into others who are prepared to attack them. Again here, fire is a great tactic, as it not only hurts them, but slows them down.
3. This is your connection. Play on servers in your country and upgrade your PC/net if possible. Also, try to get there a little faster if you want those items. Jump just after the 1 second until game starts message comes up, and sprint jump to the chest. If you rarely get anything, you can just skip corn and get a headstart on your route.
4. Try not to reorganise items that you don't use. Personally, I keep a sword (slot 1), bow (slot 2), flint and steel (slot 3 and 4), fishing rod (slot 5), food in the rest except for the final slot and arrows in the final slot, although I usually place these items there as I get them. I leave the rest unorganised until later. When you are getting rid of junk or reorganising, get a good look around you, do a little organising, look around well again, do a little more... look around, and finish it (depending on how volatile your position is, you can be less cautious, although remember it's not a rush!). Always face in the most dangerous position as you're organising as you may be able to see someone coming in your peripherals or you might make them slow down because you're watching them (seemingly). Just break your reorganising into segments and it'll make a world of difference.