If you play against players that are way better than yourself, think of yourself as a sniper. Hide behind a wall that the other team will pass by, and shoot them in the back! Experienced players will normally follow a 'pattern' and move very fast down some 'corridors' in order to take control over the best attach/defense positions. They will look for enemies in front of them, and in 'windows' and 'bridges' where they usually position themselves. If you hide in a corner where you can see little of the arena, and where there is no cover, you have a good chance that they will pass you without noticing your presence. If you had hidden in the box (left illustration), the experienced player would have expected you and shoot you.
Some players will go for the HQ all the time to get as many points as they can. They will except resistance on the way down to the HQ, but not inside the HQ itself. It's very satisfying to see their faces when you shoot them inside the HQ, after they have fought their way through your entire team! Some arenas don't have a 'room' for the HQ. Talk with the manager and ask them to build walls around the HQ!
Roll on the floor
This technique is not very popular among the arena managers, as you can easily break the q-zar west if you are careless. It is however very effective. If a player is about to attack you, and you have no place to take cover, fall down on the floor and roll out under the attacker and shoot him. He will have his gun aimed at where he expects to find your west, and will be afraid to fall over you when he notice your position. You will therefore normally have plenty of time to shoot him. Make sure to cover your face with the gun, in case he steps on you (I have not experienced any physical contact using this technique - and I use it quite often). An experienced player that is taken down this way by a less experienced player will most likely be angry. That's to your benefit, as angry players are more careless, and easier to hit.
Massive Attack - how to defend yourself
Sometimes you will be in a situation where several opponents are attacking you. What's important is to know how many they are, where they are, and then make a quick plan of how to take them out. Making a counter attack (alone) will most likely get you shoot (unless you are very fast and experienced). The other day I was defending the HQ, and had 3 experienced players attacking me. I was tired and slow, and had no chance to take them out in a counter attack. The three attackers knew that I was among the most experienced players, and attacked from 3 sides, very carefully. The illustration show how I took them out, one by one, without exposing myself to more than one 'alive' attacker at one time. The 4-step move took less than 2 seconds, and all three attackers was shoot.