French grammar is large and only a small part of it separates one CEFR level from the next. These four are that part.
Gender, and why it is not optional. Every noun is masculine or feminine, and the gender changes the article, the adjective and often the past participle. There is no way round learning it — so learn it WITH the noun, never after. Not *table* but la table. Not *problème* but le problème (it is masculine despite the *-e*, along with most nouns in *-ème*).
Patterns that are reliable enough to lean on: *-tion*, *-sion*, *-té*, *-ette*, *-ance*, *-ence* are feminine; *-age*, *-ment*, *-eau*, *-isme*, *-oir* are masculine. The exceptions are famous because they are few.
The two past tenses, which is the B1 gate. French has a completed past and a background past and uses both in the same paragraph.
- Passé composé — a finished event. *J'ai mangé. Je suis allé.*
- Imparfait — what was going on, what used to happen, description. *Je mangeais quand il est arrivé.*
The test is not time but aspect: did it happen (composé) or was it happening (imparfait). Getting this wrong is the clearest signal of a B1 candidate writing at A2, and getting it right is the clearest signal of the opposite.
And the auxiliary: most verbs take *avoir*, but a set of movement and change-of-state verbs takes *être* — and with *être* the participle agrees with the subject. *Elle est allée.*
Pronouns, and their order. *Le, la, les, lui, leur, y, en.* They go BEFORE the verb, which is the opposite of English and the thing that makes French sound French. *Je le lui ai donné* — I gave it to him. Learning the order (me/te/se/nous/vous → le/la/les → lui/leur → y → en) as a fixed sequence is worth an evening.
The subjunctive, which is a B2 marker. Triggered by expressions of will, emotion, doubt and necessity: *il faut que*, *je veux que*, *bien que*, *avant que*, *je doute que*. You do not need every form — you need *que* + the present subjunctive of the common verbs, and you need to produce it once or twice in an exam piece. Examiners notice its absence.
Where to spend your time. Gender and the past tenses first, because they are in every sentence you write. Pronouns next, because they are what makes writing sound fluent rather than assembled. The subjunctive last, and only to B2 depth.