If you want to propose to a girl, the best way is to first get her in a car. Get her in the passenger seat and make sure you're the driver. This is an important detail.
First things first you want to start driving normally. Just start talking about how you love her, what you like about her, and how you dream of a future together.
Secondly, go on a highway and start building up some speed as you normally would. Get some speed up, she'll wonder where you're going, but just keep building up the suspension before finally popping the question.
This is the part that matters. This is the fork where it can go two ways.
If she answers yes, you can turn around the car and go home.
If she answers no, you should then put your foot down, violate the speed limit, speed up, tailgate, and begin swerving frantically. Your goal here is to scare the shit out of her. Start acting fucking crazy. This is important because this will get her to say yes!
Just keep going with it, do some dangerous manoeuvres and shit. You really want to keep frightening her. If she keeps on saying no, just keep accelerating and swerving frantically on the road until she says yes.
Once you have that yes, you can then slow down and go back to driving normally. You can turn the car around, go home, have some amazing sex, and then work out the details of the wedding.
Foolproof plan unless she doesn't speak a word of English