Here's a couple of tips for Berlin. Just to make it simple and clear, I try to limit myself to two tips per category. One important tip is to rent a bika (if not in winter). Some hotels have their own bikes. I usually rent one from Fat tire (at the base of the tower at Alexanderplatz), a bit on the expensive side but works. Bring an extra ID as they want to keep the ID during the rental. The second tip is to carry cash. This is still a cash city (and country), even in some fancy/expensive restaurants.
Renger-Patzsch. The odds are you're the only turist here; this is a bit off the normal streets. Well worth the walk. Solid and I just love the interior and looks. The food is on the same level. Always go for the daily 3-set menu.
Roberta kocht. South German food. A tiny place that makes you feel welcome and almost at home. Lovely food from a very short menu.
Zola. Napolitan style rules! Roman pizza is very thin, a napolitan is doughy with an almost burned thick crust around.
Big stuff smoked BBQ. Friendly staff in everyone's favourite food hall (Markthalle Neun). The combo platter is a must, but the sandwiches are a good starting point for your next addiction to come.
Silo coffee. One of the best breakfasts I've had. Basic looks but just right.
A Horn, especially nice when you sit outside but works all year round.
The Barn. I'm not sure I even like the 3rd wave stuff (who like weak coffee?) but it is a nice place, a roastery, well brewed and with a sense of style, and they have a laptop ban!
Einstein Stammhaus, coffee vienna style. You can eat breakfast, lunch, dinner or have drinks here. Solid.
Litteraturhaus, traditional café with excellent service. Winter garten and in a classical style.
Zeit für Brot, a bakery and a popular one. Excellent breakfast if you are into bread.