I have three older teenage characters, one is from a obscenely rich family who doesn't like him for who he is, one is some kind of witch/thought manipulator and works in a gelato shop - these two share an interest in music, and attend a private boys school. The third character was adopted (but doesn't know because the memories from her previous life are wiped), and she can bring stuff from dreams into reality - but she doesn't know that, only knows that her dreams are hyper realistic and often foretell the furture. Somehow she needs a mentor to teach her how to take stuff from her dreams - or maybe not, are there problems with that?
It's set in a town/city in roughly modernish times.
Only issue is I have no idea what the plot is…please, any ideas?
Hmmm, I guess some blanket advice would be the introduction of a villain/villainous group. If this is a world of magic, even if only a few have it/ know about it it doesn't seem unrealistic that magic users would form alliances with each other for good, evil, chaos etc. You could try something along the lines of another Magic user who is part of some kind of clan or team senses your characters' awakening powers and seeks them out to join them. It could be your characters are recruited by or the good guy or switch it up and have them recruited by the bad guys who are masquerading as being good and your characters slowly realize they're on the wrong side of history and fight against the people who formally trained them. And then you get to balance all this external drama with their individual personal drama of family friends feelings etc