Okay, so first you'll need a decent amount of points with each girl to open up most paths, so so take that as a precursor to everything below. Points are easy enough to accumulate, just be nice/friendly in most cases and you'll get enough points. In some cases you won't be able to pursue multiple girls in one playthrough, so if you're aiming for a specific girl prioritize her over all others just to be safe.
To get onto Tegan's path you need to pick her over Rosie to be a geography study partner.
Bobbie's path gets started when you say "You think so?" to Jess after the Bobbie/Bonnie beer pong scene.
Bonnie's path can get started at the same time by saying instead "I think I prefer Bonnie" but there will be another onboarding moment later, too. (but right now there's no bonnie path/content yet, but that is technically a start point)
For Imogen's path you need to kiss her at the skatepark.
That's it for now for main girls (Alice, Ava, Ellie are all still to come - though technically getting Ellie's nude during the pledge week would be smart for her, but it's not a path starter). Then for side girl scenes so far, you need to have Chloe win the twerk competition to unlock the opportunity for her scene; for Lucy's scene you need to have gotten her nude in the pledge week, then flirt with her at the gym; for Mariah's scene you need to lose beer pong to Lucy; and Lauren's scene is optional if you don't have sex with Tegan during the pledge week but still want to be the one to complete the task.
That's about it, for now, I believe. Let me know if you've still got any questions, I'm always more than happy to help!