Learn French: La veille du départ, nous étions nerveux. - The day before the departure, we were nervous.

La veille is the standard, most natural way to say "the day before" or "the eve" of an event in French. While le jour d'avant is sometimes used, la veille is the dedicated and preferred noun for the day immediately preceding a specific milestone.

Why is the imperfect tense (nous étions) used here instead of the passé composé (nous avons été)?

The imperfect is used because being nervous is an ongoing state of mind or a description of the background scene. The passé composé (nous avons été) would imply a sudden, completed action, sounding more like "we suddenly became nervous" at a specific moment.

Since nous is plural, why doesn't nerveux have an 's' added to the end?

Masculine adjectives that already end in -x in the singular (like nerveux, heureux, curieux) do not change their spelling in the plural. However, if nous referred to a group of only women, you would use the feminine plural form: nerveuses.

Why isn't there a preposition at the beginning of the sentence to translate "On" (as in "On the day before")?