Yeah, you'll see. I went out a few times in the Bastille area and we basically took a walk and choose where we wanted to go just feeling the atmosphere.
For pubs/cafés, look at the terraces if they are full or not, if people are talking. Look at the interior or listen to the music and if it pleases you and enter one. Drinks are kinda expensive though, beware. 5/6 € average for mojitos, if you can, get in during happy hours.
But there are also plenty of cozy/jazz bars if you just want to spend an evening/night with you and your girl in a quieter place
Anyway, how's your french ?