There are no sounds in the Church Slavonic language that do not exist in the Russian language.
Basically, the general rule applies: it is read as it is written. “What”, not “what”, “on him”, not “on the field”, and so on. When reading Church Slavonic, you will have to constantly struggle with your own pronunciation habits. Don’t forget that even if you read “to yourself,” the so-called inner speech works, in which both correct and incorrect pronunciations are reinforced. In particular, this is also why beginners are not recommended to read prayers “to themselves”, but are encouraged to read everything out loud, slowly, with attention to every word.
No “e”! We are so accustomed to them that they sometimes slip through even in the readings of fairly experienced church readers. Watch yourself: “mine”, “yours”, not “mine”, “yours”; “calling”, not “calling”, “tears”, not “tears”, “dead”, not “dead”, and so on.