if your walking with your girl in the park, stop in a pretty spot, get on one knee, take her hand and say "Emily, will you wait for me.....as i tie my shoe?"
A Friend of mine proposed like this one time while drunk when his girlfriend was complaining about how he would never ask her to marry her one night. Except instead of a note saying made you love me, he asked her to get him a beer. I almost peed myself laughing. Poor girl.