Russian learner mistakes cluster predictably around cases, aspect, and stress. Knowing them in advance makes them far easier to catch.
Reading В, Н, or Р with their Latin sounds instead of their actual Cyrillic sounds — see Russian Alphabet Explained.
Since stress isn't marked in text, guessing rather than checking leads to consistent, compounding pronunciation errors.
Forgetting that 1 takes nominative, 2–4 take genitive singular, and 5+ take genitive plural — see Russian Numbers.
Using perfective and imperfective verbs interchangeably loses a real, meaningful grammatical distinction.
Russian past-tense verbs agree with the subject's gender — a detail easy to forget when gender isn't marked on the verb in other tenses.
Inserting a present-tense "to be" where Russian grammar expects none, carrying over an English sentence habit.
Treating hard and soft consonants as the same sound, losing a real, meaning-distinguishing feature.
This overwhelms most beginners; nominative and accusative first is the more effective sequence.
Some cursive letterforms differ substantially from print, surprising learners who haven't practiced both.
Defaulting to simpler forms and continuing builds real fluency faster than waiting for grammatical certainty.
See also the reference page: Russian Grammar.
Mispronouncing Cyrillic letters that look like Latin letters (В, Н, Р) using their Latin sounds instead of their actual Cyrillic pronunciation.
Because stress isn't marked in standard text, guessing rather than checking leads to consistent, compounding pronunciation errors across many words.
Forgetting that different numbers require different noun cases — 1 takes nominative, 2-4 take genitive singular, and 5 and above take genitive plural.
Yes — treating them as interchangeable loses a real, meaningful grammatical distinction between completed and ongoing/repeated actions.