Singular noun declension rules.
The first declension group is for FEMININE and masculine nouns that end in -а и -я.
The second declension group is for MASCULINE zero endings (consonants or ь), and neuter nouns ending in -о и -е.
The third declension group is for FEMININE nouns with zero ending -ь.
Why is it important to drill?
When creating sentences using prepositions, many prepositions are already categorized by CASES (nominative, genitive, dative, accusative, instrumental, and prepositional). It does mean that you have to recognize TWO (2) things before being able to move forward with your sentence:
The required case based on the preposition
The gender of the noun
Knowing those two bits of information will tell you exactly where to look if you use charts.
Not to mention, you will be able to recognize which case the noun needs to be when you’re reading passages, which will help in understanding the structure of sentences (and a little into their minds тоже). We all know I like this can be structured as мне нравится этот. The noun or subject (I), is in the dative case. The object is in the infinitive. (And the verb is reflexive, which is WHY the subject is dative in the first place, but more on that behemoth on another post).
(anyway...refer back to this until it becomes second nature.)
(next up: verb conjugations, also three types)