Lots of great tips here, but one that works pretty well for my group, is to think of myself less as an actor playing a character, and more like a narrator. Which is to say, I’ll often describe the actions and/or thought process of my character before saying what I think they’ll say (in my normal voice).
This is easiest for mages since cantrips like Prestidigitation become powerful roleplaying tools, but even something like holding a Fire Bolt in the air over the person you’re trying to intimidate can have an interesting affect on the mood of the scene.