Whenever people think of John Rambo, they see images of a badass soldier, who without hesitation or fear, dives into the battlefield with guns blazing. While he is certainly not afraid to mix it up in front of enemy fire, Rambo is really more of a tactical fighter than a straight up shooter. If you remember the Rambo movies, he spends most of his time ambushing his enemies or camping at a strategic location and picking off baddies from there. Only towards the end of the movie does he lay the smackdown and really give it to them. Now, I don't come up with Wolfenstein strategies from watching Rambo, but I bring it up to make a point: use your head before using your gun. By carefully camping at strategic locations, you can kill lots more baddies and suffer fewers deaths.
Medic Shields
The first thing you should do when setting up camp anywhere is to use medic shields. A medic shield is a bunch of medic packs laying on the ground right in front of you. Whenever an enemy injures you, you can just run to a medic pack and revive your health that way. This method is a lot faster than taking out medic packs and doing it one by one. In essense, your medic packs act as a shield, giving you the ability to take vastly more damage. If you have enough packs, you can easily double your HP. With that much health, your medic will be virtually impossible to take down.
Cover
As a medic you can regenerate. Cover, or things that obstruct your enemy's view of you, can buy you time to heal. Make sure your camp location has enough cover to provide a good hiding place from enemy eyes and bullets.
Traffic
In selecting a camp location, make sure there's enough traffic for you to handle. It's not very productive to be camping at a location where no enemies shows up. You want just the right amount of traffic, but not too much though. You can be easily overwhelmed if everyone comes at you. How much is too much is really up to you. If you're a new player, try to find 1-on-1 locations where you can easily take them on. If you're more confident, you might try taking on two or three at a time. For me, I try to find as many 1-on-1 situations as possible. Unless I'm 100% sure I can take on multiple guys and win, I won't rush in.
Height
It is always preferrable to be taller than your enemy. The ideal camp location will be up on a hill and your enemies will be down in the valley. It is much easier to pick off your enemy when you're looking down. You get a panoramic view of everything. You see all the nooks and places they're hiding behind. Conversely, it's much harder for them to see you because you can easily hide behind a rock and they wouldn't know where you are.
Also, when you're high up, it makes attacking you very difficult. Moving up a hill is a lot harder than moving down so when they come up to attack you, you can shoot them down easily because they're moving so slowly. Thus, ideal camp locations are usually in tall places.
Choke points
A choke point is where the enemy comes out of, like a doorway in front of the spawn. Ideally, you want a camp location with only one choke point. This means that the enemy can only attack you from one location. Having fewer choke points means fewer areas to cover. Afterall you can only shoot one spot at a time.
A bad location will be one where the choke points are out of your view. An example is one where there's a choke point in front of you and one in back. You can't see in the back so your backside is very vulnerable. Avoid these camp locations at all cost.
Ambush
The easiest way to kill your enemy is to shoot him when he's not looking. Yeah, it's a cheap way to do it, but this is war. No time for playing fair. These camp locations are usually located behind a spawn area. You can get a lot of kills using this method. About a third of my frags come from this method.
If someone has better gunning skills than you, this method works wonders. Any great gunner who is attacked from behind will have a hard time recovering.
Escape Route
All great camp locations must have an escape route in case you need to run away. You want to avoid corners, small rooms, and tight hallways because of this. If you camp at a place long enough, they're going to notice and send the whole army after you. During which time, you better run!
Conclusion
These are some of the criteria I use in selecting a camp location. I get most of my kills from these set locations. Once a camp ground has dried up, meaning all enemies are cleared, I move on to another one. Each map will have set places where you can camp. Look carefully for them. By camping there, you can make your job of picking off baddies an easy one. You'll become a regular Rambo in no time!