Yeah I feel you. I'm doing two campaigns right now, one is my first time as a player and the other is the first time as a DM haha, as a player I'm a bard so the face of the party and my old-school improv skills are getting tested for sure!

Personally I find fleshing out your character's backstory makes playing them a lot easier. If you know your character inside and out, you don't have to translate an event into their "language" and think about what they would do or say from their perspective, you just let the thing happen and the character will tell you how they respond.