Tegel Airport: tinier than you imagine it would be
Berlin is an odd European capital city in that it's airports (Tegel, Schoenefeld and the now closed Tempelhof) are all about the size you'd expect of an airport on a small tropical island somewhere. We're talking a distance of about fifty metres from the check -in counter, through the gate and onto your seat in the plane.
The main building (Terminal A) is a hexagon, which you can see on this image, and the gates are arranged around it. This gives Tegel a few rather unique peculiarities, the primary one being that check-in and pick up occur directly at the gate. Rather than banks of counters at an entrance to the airport, you line up directly in front of your gate, check in and then move about three metres right or left and go straight through into the waiting lounge. Each lounge has its own security set up - no huge lines as your plane has it's own machine.
Arriving is just as personal. Immigration is waiting a few metres from the plane and directly at the carousel where your luggage will appear. And five metres further on is a big glass window where those waiting to pick you up will watch and wave. I must admit I usually stay hidden from the window as what undoubtedly ensues is ten minutes of waving, exaggerated facial expressions and attempts to silently mouth out greetings. It can be kind of embarrassing, so I usually hide back a bit until the bags start appearing.
Now, Tegel has expanded from the original hexagon and now includes several other terminals (see this map). Although none are more than a few hundred metres away (notably Terminal C is a bit of a hike outside) it can be a bit difficult to spot the others. Follow the signs and don't mind if they appear to be taking you to a small doorway or down to the cellar. These follow the more common layout of a primary check-in area and then the individual gates.
Because of its odd arrangement, there really is no central place to gather, shop and eat in Tegel. There is a restaurant at the front of the hexagon called Leysieffer, a chain bistro you can find at several other German airports. A different eatery is halfway around the hexagon and is more of a 'grab a tray and pick up the plate' joint, with a Segafredo cafe and a bar nearby. Upstairs at the front of the terminal are the airline lounges and the Take-Off bar which is a good place to get away from the crowds downstairs. As with all airports, pricing is steep and expect to pay upwards of 10€ for any warm meal you might like to have. There is a Burger King and, next to it, a supermarket/deli which does some decent sandwiches. In Terminal C you'll find a few coffee and food shops to help you pass the time but make sure you have your own book already - the range of English books, magazines and newspapers is extremely limited.