I spend a lot of time in Prague and I haven't come across anyone who takes Euros. ATMs when you get there are your best answer - Czech Koruny are readily available over the counter here at any Bureau de Change, so get a few quids worth to see you over the first day or so. Standard tipping practice is to round up your bill to the next convenient round figure; huge tips are not necessary or expected. Sterling is easy to change in Prague, but you'll get a better rate at an ATM. I was last there in November, and the exchange rate was about 40 Koruny to the pound.