We went to Berlin last summer.

A river trip is worthwhile. You get to see the city from a different angle.

Get yourself a three day tourist ticket for the public transport. Unlimited travel on bus, trams, U-bahn and S-bahn at a very reasonable price. It also comes with vouchers for reductions on a whole host of attractions. We got a useful reduction on the river trip.

We found a flyer in our hotel for a guided city tour with commentary in English. It was run by a South African whose wife was a Berliner. He gave a different perspective from the bus city tours and went to places the bus tours didn't.

Enjoy yourself. There is plenty to do and see. We found Berlin a very laid back city.