Use an emphatic correlative structure.
Use a past perfect idea before another past action.
Use concessive and causal links naturally.
Use a cleft-style subject phrase.
Use the unreal past conditional.
Use a formal but natural register.
Use a time expression showing immediate sequence.
Use a negative condition and a concession.
Use an imperfect background clause and a passé composé/main result.
Contrast fluency with remaining errors.