From the airport - if it is not a taxi (trip around PLN 80, c. 20 euros) - take the shuttle train (tickets on board or from vending machine in arrival terminal) to the main train/bus station.
Because of constraction work, this summer there is no direct tram connection.
Walking from the train/bus station takes approximately 15 minutes. You need to get to the underground passage situated in front of the ancient main train station building. Leaving to the left, take ulica Westerplatte and get to the big Post Office building, then take a left into ulica Starowislna (not to confuse with ulica Wielopole), cross ulica Dietla and straight along ulica Starowislna get to ulica Miodowa. Now you only need to take a right and proceed to number 28.
Taxi stands are located above train station platforms, in front of the bus station building, or in front of the shopping centre. Expect to pay no more then around PLN 20 (c. 5 euros).