We have been to Prague three times and have obtained local currency from ATMs both at the airport and banks on the streets. Use an ATM/debit card from your bank or credit union, and before leaving the US, inform them of your travel locations so they don't freeze your card due to suspected fraud.
It would also be best to carry two ATM/debit cards in the event one card is frozen. We just returned from the UK, where in spite of informing of our travels, withdrawals were frozen for one of our cards.
While in Prague, we have taken both trams and subway without a currency problem. As with any foreign country where stops are named in their native language, note the spelling on a map of the transit system so you know where you are and when to get off.