The way my boyfriend did it a week ago.
He didn't take me to a ball game and have it displayed on a blimp or JumboTron. He didn't hire a singing telegram or make a cheesey machinima youtube video. None of that weird stuff that guys do to make it impossible for the guy or girl to say no even if he or she doesn't really want to say yes.
He just told me in a very sweet way what I mean to him and asked me to make it legal. He surprised me with love and honesty, and made my heart soar.