Great job! Management of a-fib is a bread-and-butter skill for inpatient neurology, with it being so common amongst our stroke patients.
If they're unstable (e.g. hypotensive, demonstrating signs of shock, endorsing chest pain), then follow the ACLS algorithm and immediately perform a synchronized cardioversion.
If you're absolutely sure the patient has never before had a-fib, and they newly develop it before your very eyes, it's reasonable to give cardioversion a try so as to minimize the future risk of a-fib ("a-fib begets a-fib"). Otherwise, usually we have to err on the side of assuming that they've had paroxysmal a-fib for > 48 hours, so we'd have to preferentially focus on rate control. However, rate control with the usual beta-blockers (i.e. metoprolol) or calcium channel blockers (i.e. diltiazem) can negatively impair cardiac function, so we also need to pay close attention to the patient's cardiac function. (It might be worth trying digoxin, though your mileage may vary. It also takes time to become effective.) A formal TTE would give us an idea of their LV and RV systolic function. Clinical signs like JVD/JVP elevation, peripheral edema, and hepatojugular reflux all suggest decompensated heart failure, in which case we'd have to change gears and just use amiodarone.