One of the most important choices you have to make before you arrive in the Czech Republic is to pick the right language course. I've heard a lot of stories about people paying a great amount of money almost for nothing. You have two options: private or public courses. Each of them has its benefits and disadvantages.
Public courses are cheaper, but you have to find a dormitory or a flat to rent. And you usually have to deal with problems on your own. I can say, that when you are asking someone for help you'll rarely receive a negative answer. My teachers were always willing to help with any problems even if it wasn't related to studying.
I picked public courses in Pilsen. I knew that I wanted to study at the university there so it was a perfect choice for me. I passed the B1 test with 93.6 points. One of my friends had a mark that was different from mine by less than one point. And he is not from Slavic country.
So be attentive to the details when you are looking for a course. You can choose to study Czech in Prague. You will be satisfied and excited about Prague. But from my own experience, I recommend that you also consider studying in smaller cities. In terms of practising the language, you have a fair chance to practice and get better everyday because you get to speak with locals a lot, while in Prague it will be hard to resist speaking Russian or English outside of school.
Good luck!