I cant stand cartomizers, they jack up the taste too much, so I'm a die hard atty fan. You don't need to clean your atomizers often, but when you do clean them, use this method (I seriously have atomizers that are 7-9 months old):
Take the atomizer off the battery and blow super hard into the battery end, this blows nasty old juice out of the screen in the bottom back up into the coil.
Put the atty back on and vape it a few times until you get less vapor, and dont inhale this vapor, it will taste bad, just blow it out of your mouth.
Do that a few times until you dont get any vapor anymore
Now, you can dry burn the atomizer if you want, some people think that this helps... Dry burning is just keeping your finger on the button over and over to burn junk off the coil in the atomizer.
What I like to do is get some crest pro mouthwash (its blue, and doesnt contain alcohol) and heat it up for 30 seconds or whatever in the microwave. Soak your atties in that for 15 minutes or so, and kinda shake it gently every once in a while. I dont know what the deal is, but this stuff cleans the crap out of your atomizers... Ive tried peroxide, rubbing alcohol, denture crap, whatever, this works the best.
Its super important to rinse your atties really good after this, using warm water. Its critical to suck water through the atomizer with your mouth over and over to get everything out too. Rinse them super good, maybe even soak them for a couple hours. The let them dry... You can do that overnight but if you are in a hurry just use a blowdryer.
The next super important thing is priming them correctly once they are clean... drip a few drops of juice on the atomizer and then just take a couple puffs... drip a few more drops on and take a couple puffs. By this time it will most likely be primed.
I hope this helps someone lol, Atomizers last way longer than people think, and when you clean them good, they perform like brand new.