You can easily exploit the threesome actions to make any character get points with you. What you usually do is call up Rogue or another character you already can do stuff with. Ask them to either have a threesome or dance for you... basically any action that has 2 girls together. You will always get rejected by the second girl who you are trying to seduce. After that just start having sex with the girl you already have a good relationship with... The second girl will get aroused and will either start masturbating or eventually join you herself.
For instance I used Kitty to seduce both Emma and Laura. I had sex with Emma a bunch of times before I even got the event where she was masturbating in the classroom by just asking Kitty to dance or strip with Emma or for them to make out. Emma rejected most of the request to make out or strip... but you just keep having Rogue or Kitty strip or do something with you till the other girl gets aroused enough and joins in... or just gets enough inhibition.
As for the normal way without exploiting the threesome mechanics. You just keep flirting with them until they have like 400-500 love so that you can touch them...give them messages or touch their thighs until they get aroused enough then ask to shift your actions to like a blowjob or finger them, etc...
You can also just keep asking them to do something that you know they will reject. Then keep replying "maybe later" for a lot of easy love points. Ask them to do everything once every part of the day, so they don't get annoyed with you. Usually the titjob, handjob, footjob, and blowjob options... you can ask one of the girls to give you a blowjob and they will usually turn down the idea, then chose the middle option of "begging / please"... a lot of times they will say "can I give you a handjob instead?", accept it then do some off hand action with them or just keep pressing continue until they get slightly aroused, then chose the shift action option to get the blowjob or titjob that you wanted. Which gives you easy amount of inhibition and obedience.
Also whenever possible get them a dildo and gift it to them. I believe it gives an easy +40 of every state. Though they get kind of annoying since the girls will always pull out a dildo and masturbate while you're having sex. So if you don't want them to constantly use a Vibrator or Dildo to show you how woefully inadequate you are, then don't give it to them.