Mikey is our business expert who knows that the customer is always right and in your case, you're the customer to your SO.  So, best approach is to teach your SO yourself that way you're sure to get it right.

Just visit your favorite dildo store and find one that closely resembles your junk.  If you're into having your balls licked, make sure your fake junk has some of those too.  Strap it onto your SO and be sure to first tell her what you're gonna do, splain it by example, and then tell her what she should have learned.  Typical training course, right?  Tell her how your going to slide it gently into your throat, clamping your lips at the base with a slight rythmic sort of motion all the while breathing through your nose.  Explain how it's only uncomfortable for a moment but the "DT'er " quickly gets used to it.  Be sure and mention that your junk isn't too large so she may only feel a slight rubbing against her tonsel.  Tell her how you are going to simulate the final swallowing but when she does it for real, it will be a warm gooey mixture that quickly disappears with an unusual taste once she uses the saliva below her tongue to wash it down.  Be sure you maintain eye contact during it all so that you know she is paying attention.  Following this, you might even want to expand the lesson by coaching her to stick it in your ass, gently and slowly, right, so that when your interests change, she will already be "trained".

That should cover it, and just think of all the money you saved by doing it yourself.