I have to admire all foreigners learning Czech or Slovak language. You can use these languages only in the region of former Czechoslovakia and they are really difficult to learn. Well, my native language is Slovak, but I was growing up in former Czechoslovakia and I can communicate in Czech if necessary. However, I have no clue about Czech grammar rules and I need a lot of practise to reach correct pronunciation. To be honest, I'm not sure about grammar even in my native language.
For those obsessed with languages. Czech language is pretty similar to Slovenian, on the other hand, Slovak language is much closer to Croatian. But in general, all Slavic languages have difficult grammar (at least 7 cases, declension of nouns, adjectives, pronouns and numerals dependent on gender, number and case). Of course, this also depends on local dialect. I mean, nobody cares about official declension rules during informal conversation.
I guess, the best way how to learn correct declension is to watch a lot of Czech TV programmes and after some time you'll get some feeling for what is right and what is wrong. But beware, there are many informal (and gramatically incorrect) uses of Czech language in TV. I'm watching a lot of Czech programmes and in many cases I'm in doubt whether the declension I'm going to use (so commonly used in TV shows) is gramatically correct or not. I don't know why, but this is not the case of Slovak TV shows. Contrariwise the language used there is too gramatically perfect and looks pretty unnatural. Maybe it's a negative influence of so-called language law, which strictly constraints the language used in Slovak media.
Anyway, there is quite good reason why to learn Czech language. The Czech movies are jewels of European cinematography and the one who can watch Czech movies in original version is blessed. Even Czech dubbing is great. French actor Louis de Funés himself confirmed, that the voice of Czech actor Frantisek Filipovsky (who was dubbing de Funés in most of his comedies) was even better than his own.