First of all; I took the liberty to move the topic to the strategies & tactics forum.
Now, some quick feedback on your game is (with only a very brief look on what the others have written, so might be pretty much the same feedback).
Prioritize the top tier weapons harder. By "top tier" i mean rocket launcher, lightning gun and perhaps grenade launcher. With your > 100ms ping i might even suggest that you put less focus on the lightning gun as it will be hard to hit with that anyway, so your top focus should definitely be the rocket launcher - get to know the maps so you can get to the rocket launcher and its ammo (don't forget that the grenade launcher also serves as rocket launcher ammo) even when blind folded!
Prioritize the armours a lot more! Especially on DM6, which was the map that the demo was from, you should strive to get control of the red armour area and pretty much camp it. Perhaps not camp exactly by the red armour, but keep track of when it spawns (i.e. 20 seconds after it was last picked up) and keep watch by the grenade launcher during the time it's not spawning. If you're not in control, then you need to stack up on green armour, megahealth and a rocket launcher and try to do hit and run damage until you find the opportunity to take over the red armour. Never attack without armour and rocket launcher unless you think your opponent is in REALLY bad shape (i.e. he has like 5 health left, which rarely happens?).
Don't waste as much ammo as you did in the demo - make sure that every rocket (or grenade as they use the same ammo) is a well spent one. This is extra important on DM6 compared to the other standard maps as there is very little ammo available; 5 rockets from the rocket launcher (which you can't pick up a second time unless you have died), 5 rockets from the grenade launcher (which the opponent might be in control of) and then there is the 5 rocket pack by the green armour, which usually the player that is not in control of the map (i.e. red armour) has access to.
Listen to sounds to get better awareness about your opponents' whereabouts - this makes it possible to place prediction shots which will hurt your enemy before he even sees you. This makes sure you won't get surprised, and you will be better at not wasting ammo.
Time items to get an advantage on your enemy. Makes it easier to plan your game overall, knowing when to attack etc. For a start i think you should focus on timing the red armour on DM6 though, i think that will help your game alot.
A last and perhaps somewhat controversial tip would be: play to win. By this i mean that you should play defense when you have to in order to avoid getting fragged, and play offense when you really think you're at an advantage (or really need to gain frags because you're already below by a lot). It might sound obvious, but often new players play a bit naive, but if you watch demos of the really good players you will notice that they rarely give anything to their opponent for free. Usually the game will also be alot more enjoyable when winning. Don't forget to also have fun though.
Good luck in your future Quakeworld endeveaours!