Just recall that most of the instruction available in English is about how to pronounce Slavonic like a Russian. And that the world is full of people who firmly believe that the Russian pronunciation is the correct pronunciation, the way Cyril and Methodius pronounced it, and any deviation is some sort of mistake or a symptom of perverse nationalism.
This is nonsense, but you will encounter it as an article of faith in many minds.
The Ukrainian pronunciation is not the same as the Russian; the Rusyn pronunciation is not exactly like that of the Ukrainians; the Serbs do it their way; and so on and so on.
Stephen