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).I found going for mind control 2 asap and changing everyone's personality to one type makes things so much easier. Another option is to go for SymPathic Link level 2 for the Gift of gab ability so you don't have to memorize what their interests are.
Studying at home can improve grades. I find the first month is a pain and makes the MC and mother look like idiots as they don't check on what the requirements are before getting the MC's power so they can deal with the grade issue.
I really like the game but I wish there was more about this world the MC lives in as it has issues that ours wouldn't have. Like for example, there are cell phones but no evidence anyone has even heard of the internet. Of course this could be homage to superhero comics where when one really sits down and looks at it makes no sense from a social or technological point of view. There is even a name for this trope: "Reed Richards Is Useless".
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.