* Your FIRST priority in CTF is the flag. If you are worried about your K/D, then go play Elimination or something... Anyways, if you don't feel like running after the flag, STAY and GUARD your team's flag.
* If the other team grabs your flag, make sure to CHASE them. Don't stand around and hunt enemies for kills. The flag is always your main priority.
* If there is a loose flag, RUN for it. It doesn't matter if its yours or the enemies. If its the enemies you may score a point for your team. If its your flag, you get a recovery point.
* If you have the enemy's flag, but your flag is taken, hide and wait for your teammates to recover your flag.
* Use smoke grenades. They are very helpful when rushing for the enemies flag. Toss one near the enemies flag stand for some great cover. Make sure to wait a second or two after you throw it, because of the slight delay before the smoke comes out. However, Make sure NOT to smoke your own base. This just gives the enemy free cover. Also, try to keep watch for grenades thrown into the smoke - they're pretty hard to see.
Please note that the use of smoke grenades is controversial. It does gives you cover to run in and grab the flag, but then after that you have a flag icon above your head. This causes you to be unable to see any enemies, but they all know where you are. Plus, any nearby teammates can't provide cover fire since your smoke is blocking any line of sight they would have had. If the other team knows what they are doing, they can just kill you through the smoke and recover the flag.
* Use mines.* Mine your own flags base. Place them all around your flag. When the enemy rushes for your flag, they will likely be killed or seriously injured because of mines. Be careful not to step on your own mines - they will kill you and maybe your teammates (if friendly fire is on).