Berlin has A LOT of construction going on all over the city right now. For example, Gendarmenmarkt square is completely torn up and inaccessible, as is the Platz der Republik in front of the Reichstag.
If you don't already know, the Pergamon and German History Museum (main collection) are closed for renovation. That said, the Pergamon Panorama is a really interesting experience and worth a visit. Gemaldegalerie is fully open, however, and currently featuring a great Franz Hals special exhibition.
S-Bahn rail line out to City West sights is currently closed for repairs (signage for alternative ways to get to the Zoo, for example, are difficult to interpret unless you are pretty fluent in German). Take U-bahn or bus to City West instead.
Getting around: Using the BVG mobile app on my phone was a piece of cake and made it very easy to purchase transit tickets (we used the 24-hour small group pass almost daily). Highly recommended. We also used Uber a handful of times when the heat and humidity made the U and S bahn trains too much to bear.
Lodging: Our family of 5 stayed in a three-bedroom apartment at The Circus Apartments near Rosenthaler Platz (U-Bahn and tram hub) and it was ideal lodging with a great cafe attached for breakfast. The apartments are managed so all the amenities of a hotel including concierge and cleaning services are included. They even offer free guided tours (we signed up for the Topography of Terror visit and it was really well done).
Food tip: Had not been to Prater beer garden in Prenzlauer Berg on previous trips and was kicking myself - so fun and convivial, easy and efficient with great beer and grub for an absolute bargain.
Lastly, the new Berlin airport is an absolute dream compared to old and dreary Tegel. Clean, efficient, tons of food and shopping options, and did not feel crowded at all upon our arrival or departure.