Manipulating earth itself to do various things, gravity and magnetism as you mention, also, lightning can be Earth magic. That's a pretty big thematic scope to play with, IMO.
So...you can pretty much whatever you want?
I mean, name a thing you'd like to do, and you can likely use one of the things I just listed to do it. Usually more than one.
Attacks? Earth shockwave, bouncing metal ball of death (or Harry's attack-keys), direct gravitic assault,or lightning bolt. Stalagmites sprouting at them from the ground. Almost anything.
Defensive Blocks? Wall of earth, gravitic warping effect, magnetic forcefield ala Magneto, floating blades that parry attacks for you, etc.
Offensive Blocks? Trapping people with magnetism or gravitic force, burying them up to their necks, wrapping them in chains, etc.
Maneuvers? Well, a lot of the things listed above could be maneuvers too, also knocking people down with earthquakes, casual disarming of entire zones with magnetism, reshaping the terrain to put up scene aspects. All sorts of stuff.