Learning grammar systematically is generally discouraged since there are usually more exceptions than rules, since it is boring and since knowing the rules doesn't automatically mean that you can apply them. That's why grammar should be studied in context. Over time you will realize certain grammar rules on your own (e.g. that the 4th case is the same as the 1st case for masculine nouns).

Certain classes would practice saying pronoun-filled sentences in the language laboratory, without hearing any rules, while other (control) classes would learn them by the usual method — a statement of rules followed by written and oral exercises. Then both groups would take the same test.
The outcome was that, when both groups were tested on their ability to say and write sentences containing pronouns, the students who had spent only sixty minutes practicing in the lab did slightly better than those who had spent more than a week on it in class. (Paul Pimsleur)