2 Answers

Propose marriage?  Proposition?  What exactly are we talking about here!
Honestly, if you are talking about proposing marriage, you should know her and be comfortable enough to simply ask the question, "Will you marry me?"   Although I do know of one guy who actually never dated a girl, but went on a lot of group outings.  He fell in love WITH her and asked her to marry him, never having even kissed her once.  She said "YES!".  I know....very unique.

You can always put on a big show (sky writing, billboard).  If I'm ever asked to marry, I would like it to be while we were having a picnic by a lake, or walking along the shore of the ocean, just the two of us doing something outdoors.  

If you're really "nuts" about her, with a flower.