As long as your commute is short you'll just be uncomfortable if you got it wrong. You can adjust the next day and try again. You're not going to get it right the first time. If you're only riding like 30 minutes and you overdress (which it sounds to me like you're going to be doing) then worst case you are too hot. No big deal.

TL;DR Trial and error.

If I wore what some of the people above suggest (and my commute is only 30 minutes) I'd be sweating up a storm.