my god, the genitive case seems to be overused in russian. here is what i know so far, tell me if i'm correct:
you have to use the genitive case:
*after mnogo and the likes: mnogo predmetev
*when the direct object is a person: ia znaiu borisa i eleny
*after the verb khotet: i khotshu vody
*when the sentence is in the negative form (but it's more of a blur to me):
ia ne ponial etogo glagola.
but:
ia ne ponimaya etu frasu (i'm think when the direct object is feminine, you should use the accusative).
no idea about plural
*i'm lost with numbers:
2, 3, 4 umnix utchenika? (gen sing-gen plur because it's masculine)
2, 3, 4 belye rozy? (acc plur because it's feminine).
5 umnix utchenikov? (gen plur-gen plur)
5 belye rozy (acc plur)
no difference whether it's a person or an object, right?
there are other rules, some i'm sure i know, some i don't even know the existence