English is widely spoken in Krakow. My Polish colleagues laughed when I said that I had a Polish dictionary and I wouldn't need it - they were right, although I did try to say a few words here and there. Do not change money at the bureaus in the station or airport. You get fleeced. I found Kantor Grosz and a few others on Sławkowska str. have about the best rates. Take a little zloty with you to get from the airport to the city.
It is only a short flight, so you will only need essentials such as travel documents.
Check what facilities your hotel has, for example, do they provide shampoo and body wash and hairdryer? If you need these, take your own.
Some tourist sites can get extremely busy and you might have to book in advance - I was only there for a couple of nights and wanted to go to the castle, but it was fully booked on the day I turned up so I missed out.
There are 'free' walking tours which are worth thinking about. They don't charge, but ask for a donation at the end. The two tours I went on (One about murder in Krakow and the other around the Jewish Quarter) were excellent. Schindler's factory is worth a visit - the Jewish tour ends there so it saves time trying to find it.
Your hotel or the tourist office should have free maps, but if you have a smartphone, you can easily find places you want to visit on google maps.
Krakow is a wonderful city, but there is a lot of heartbreaking history. I didn't have time to go to Auschwitz so can't comment on that.