Is this a serious question?...or is there some level of satirical intent here?
If it's the former, then to be honest proposing to her would be a bad idea. I would not suggest it but if you're set on trying then be honest and tell her how you feel or something. If she says no, well to be fair you've lost nothing and if she says yes you've gained a ball and chain.
*ahem* wife...I totally meant wife...*looks around shiftily*
However if it's the latter then do it in the most overblown way you can think of, get a huge bouquet of flowers, take her to a romantic secluded spot where you have a picnic (or a table, with candles, a hot meal (somehow?) preferably something you know she likes, a waiter too (some snooty looking dude?) and music playing in the background (something romantic?)) and then you get down on bended knee and you pull out the ring as the fireworks you set up beforehand go off spelling across the night sky "will you marry me?". Have a friend film it all or something so if she says yes, well congratulations and you now have a nice reminder of a nice moment in your life, if she says no then you push her face into the food and run away cackling like a maniac and watch the video at your leisure. Or send into 'You've Been Framed' or something.
Alternatively...hire a barbershop quartet to sing the question or something.