for long killstreaks, there is a lot of luck involved, but also a lot of skill and strategy. thats why the best players always get the killstreaks and do best over the course of a few sessions.
maybe we can share some general tips on what we all seem to do when we have good games and maybe compare to when we have bad ones.
Whenever I get a good run going, I always find myself doing similar things that just click. I don't rush. the key is not to be faster on the trigger than the enemy, the key is to be already aiming/shooting at the enemy before you see each other i.e. experience tells you there could be some guy here or coming over here and you're already in a position to shoot that guy. Or you know he's coming to you so you ambush him.
I think one thing I seem to switch on and off subconsciously is how high I have my camera when I move, I usually have it at waist or even knee height so I have my crosshairs out of the way when I walk. This is where I get an average score cos I'll be shooting someone's legs or something and it takes that much longer to kill them. Sometimes I seem to have it much nearer enemy heads and chests so when I come to shoot, less aiming involved.
When I struggle and I start rushing, I end up getting wasted. Sometimes I get my packback and thats fine but if I kept my cool I could've come away better off. One of my better killstreaks lately was on subway (snow one?) and I was getting killed left right and center, I was like 5 deaths to 0 within a minute or something. I started off trying to run and flank, then being stealthy, then straight up SCAR-H, nothing was working, couldnt gt a read on where the enemy was coming from or going to, they were everywhere. so I decided to just sit tight and control that central corridor and help my team control the flow of the map. I held down that central corridor on my own for the rest of the game and got a 16 killstreak out of it pulling myself way back into the positives and up the ranking. Not sure if thats considered camping or not, its a pretty big space with 2 wide entrances and I wasn't exactly hiding, but I don't care, I had to stop hurting my team and it was effective.
I bet the most common killstreaks are achieved in similar ways i.e. you let the enemy come to you and if you're lucky they will just keep on coming and let you mow them down.
My friend who's a pretty average player went 33-0 on wasteland cos he was near C looking into the cave and shooting people through the wood on the other side and they just kept on coming back for more. eventually he got a chopper gunner and went to town.
claymores are my best friend, I probably get at least a 3rd of my kills from them, I'm surprised I don't see them around more often tbh. oh, important tip, if you see a team mate put down a claymore, don't put one right next to it, thats fucking stupid.