The Gift of Gab is really nice once you get it if you don't want to have to remember what topics each girl likes. You can also just socialize at lunch and use text messages to build favor, then you don't have to remember what they like. This is especially important if you don't pick Social as your primary stat (my walkthrough uses Mental for the primary).
It's actually pretty helpful to have each girl have a different personality type so you can have them train you in different stats. You gain way more stats doing that than you do going to class, especially if you're not using mods.
Aside from the Mind Control command (which I don't have yet), is there a particular trick to doing regular training with the different girls ? I have no issue with training with Mom/Sis at home but at school, morning and day training interactions are locked even at 100 favor ("Class is about to begin"). If I wait until afternoon, there you get dropped back at Home and there doesn't seem to be any phone command to interact with them in this way.
I do see a Large Favor option of skipping class but if I do that, I don't have enough Charm left to start a training session. Is that the way to do it ? I also saw a "Let's Hang out after class" favor listed on the Wiki but I can't seem to find that command either.