No tactic bro. You just do it by trying not to breathe.
Usually the smell comes from the lower part after she's badly turned on so I concentrate on the upper part trying to ignore the rest of the vagina. Put a finger inside so you'll cover the lower part and lick the upper part. It will kinda work for you but it won't be as pleasing to her.
Thankfully it doesn't happen too often. I never had a girl that always smells down there. They only smell occasionally. I have no idea why and when does it happen because it used to happen even after a bath/shower which means that it has nothing to do with hygiene.
P.S: The same is with men, I was told. We too smell sometimes and sometimes not. It's something about the hormones I think.