What is the appropriate way to propose to a girl I love, knowing that my parents refuse to reserve her for me, and should I speak to her father myself or should my father speak to him?

Marriage is the best remedy for passionate love. If the girl is religious and of good character, and you are reasonably sure she will not reject your proposal, and you can marry her soon, then propose to her. However, if any of these conditions are not met, it is better to disregard her and seek someone else, and strive to turn your heart away from her. One must adhere to the limits of interaction with a non-mahram woman; it is impermissible to speak with her except out of necessity and to the extent of that necessity, while avoiding anything that could lead to temptation.