Hackesche Höfe is a pretty cool area and all around oranienburger straße. Great place to spend an evening just wondering around from quirky bar to quirky bar. Also charlottenburg is great for nice bars, especially schwarzes café pretty much open 24/7 too.
My favourite city bar none. Helps having a Berliner girlfriend! Make full use of the s/u bahn and have plans on the things you want to do! Bring me back a curry wurst!