At the very beginning when she sees you in shower, make sure you go after her and knock on her door. When you are looking at lewd photos on computer and she sees you, don't stop. Make sure you talk to her as much as possible and go out on a movie date with her.
1-In the beginning when you first meet her, kiss her.
2-Then when you go to bathe and she sees you naked, and she run to her room go after her and knock on the door.
Those are the primary steps, in general soles be kind and thoughtful to her and continually check how your choices affect Rachel's statistics.
In addition, when James suggests spying on the girls in Rachel's room, agree to it. When you have the chance to spy on her in the shower, do so, and choose to stroke yourself when you see her. Later, when she sees you masturbating at your computer, don't stop. Let her watch. Over breakfast, when she asks if you've ever had sex, be honest (don't boast) and be sure to question her about her virginity, rather than just reassuring her. All these choices will get her corruption score up to six or seven, which is what you'll need for the relationship to start after the movie (be sure to tell her it was arousing). That night, she will come to your room, looking for company, and you'll be on your way.
There are also walk-throughs you can find online.