The trick is to inhale deeply every time you take it back into your throat. 

First lick all around the head and shaft until your tongue and is well 

coated with precum.

Suck a little more penis into your mouth each time you go down and

make sure your tongue is all the way forward under his cock. When you

get to where you feel the head of the penis at the back of your mouth

when you slide him in, pretend you are swallowing a big mouthful of

food. Time this so that you gulp at the same as the cock hits your

throat. Put the head a little further back each time and before you

realize it he will slip past the gag reflex sensor and slide all the

way down. When you feel the penis enter your throat, stop swallowing

and breathe deeply through your nose and relax. Now you can make him

cum down your throat by squeezing the penis with your throat muscles.

After a little practice its really easy. Enjoy!

The first experience for a girl who deep-throats is to keep gagging. There is 

no other way to come over it than to finally relax the throat muscles.  So your

partner should take it in real slow and to relax, maybe

swallow it a little at a time aver a couple days so that she can get used

to it.  Of course, if you're looking for an ego-stroke, you might just be

too big for her, although she should be able to take at least some of it in her throat.