It would be a good idea to have a little compass, and to get a map. If you use an ATM, suggest you ask for an odd amount, say 3900 kc (I asked for 4000 kc and got 2-2000 kc notes). Get public transit tickets from the vending machines at street level of the station, tobacco shops or ticket windows in larger stations. 20 kc tickets that allow transfers are good for 75 minutes from first validation (90 min after 8PM or on weekends), 24-hour passes are 80 kc, 3-day passes 220 kc, 7-day passes 280 kc. (20 kc~$1)
From either train station take the red "C" Metro line (direction Haje) to "Muzeum"; change to the green "A" line (direction Dejvická) and get off at "Malostranska", on the west side of the river.
Take the southbound #12 tram (direction Hlubocepy) one stop to "Malostranské námestí" (Lesser Town Square), the heart of Mala Strana (the Little Quarter), which is centered on St. Nicholas Church. The castle is directly north and uphill from here, and it's walking distance to your hotel.
Go to the northwest corner of the square and find a street called Nerudova, follow it west (parallel to the castle wall) about 250 yards to a street on the left (away from the castle) called "Jánský vršek"; "U Zlute Boty" (Yellow Boot) is Jánský vršek 11.
Have a great trip, but watch your stuff; I got my pocket picked on the Metro, but otherwise really enjoyed Prague.