Who likes getting owned in the first place? If you are not one of them... read on for some pointers that can really help you out.

DON'T:

Keep your units bunched up tightly. This makes you extremely liable to have all three get wasted by a grenade launcher or any grenade of any sort. This also limits your team's vision!
Spread the field with your units. Keep all of your units close by so that if one gets jumped, the other units can come to his/her aid quickly. There's power in numbers people!
Place your units in a straight line. Doing so will cause your team to be "lined up" for an enemy unit with an assault rifle, machine gun, or shotgun to damage all of your units at once!!
Back off when heavily wounded. You don't lose attack power or AP when in the red, and the only way to get experience is to attack, so man up and put it all on the ground! Some exceptions to this rule are snipers that are too close to the target or you have a mine you can put down.
Quit out of a game. Pulling this stunt on someone will get "n00b quitter" branded on your forehead. Also, it counts as a loss and you lose your items, not to mention that quitting systematically will decrease your rank down to widely unfamous "Deserter"!
Anger a moderator. Enough said... they keep the peace in the game. You don't bother them or anyone else, they won't slap a mute on you.

DO:

Open containers. Why not?! The only way to get stuff is to open containers.
Place mines in tight areas. If you know where an enemy is coming from, plant that mine before they arrive, get the heck out of there, then watch them swear away when they trip the stinker! Another good place for mines is unopened containers (even your dropped items are great for getting attention).
Capitalize on mistakes. If your opponent goofs by forgetting ammo or not attacking and failing to get out of your sight, you should press a counter-attack and try to make him pay dearly for that!
Collect Artifacts. These are the godsends of GUNROX, bestowing the user with cool effects or special protections. They may be temporary, but their powers are worth the trouble!
Loot other players (but not allies!). Simple really, if you are about to win, try to get some stuff before you do. You deserve SOMETHING for your troubles. Most players will drop after you start, but sometimes the server notices that and lets you finish. JUST DON'T DO THIS TO ALLIES IN TEAM GAMES, let them recover their stuff in peace!
Move diagonally whenever possible. Moving straight up and then making a move to the right costs 2 AP, but a diagonal move only costs 1 AP! This can't be done against any wall though, you'll have to go around.
When you find weapon you cant use yet (for example Benelli M3, Colt M4 or UZI) share it with your teammates who can use it.