The Temporal and Spacial Meanings of "Before": How to Get it Right in Spanish
Before Time? Before Whom or What?
The various senses of before in English and Spanish, and the types of grammatical structures they require, depend on whether it is used as an adverb, a conjunction or a preposition. Starting with a prepositional usage referring to time, consider antes de. Note that when a verb form directly follows a preposition in Spanish always, always is in the infinitive (in English, it is always the -ing form):
Antes de acostarte, cepíllate los dientes (Before going to bed, brush your teeth).
When antes is adverbial, it means before, but in the sense of first (imparting a chronology). Note that as an adverb, it modifies the verb:
Entramos antes, luego ellos entraron (We entered first, then they did).
The phrase antes de que means before and is a conjunction due to que -- which means that a clause will follow, with a conjugated verb. This expression always requires the subjunctive, because the action of that phrase is or was anticipated:
Vamos a salir antes de que llegue tu padre (Let's leave before your father arrives).
Salimos antes de que llegara tu padre (We left before your father arrived).
If antes que does not place emphasis on time or sequence, but rather a preferred course of action, then it is not a conjunction but a preposition (yes, in this case, que is acting as a preposition). In such cases it means before in the sense of rather than:
Prefiere morir antes que rendirse sin honra (He prefers to die rather than surrender without honor).
When before is spatial, not temporal or expressing a preference of one thing before another, as in the example above, delante de is used. It means before in the sense of in front of, or ahead of:
Ellos se sentaron delante del professor (They sat down in front of the professor).
Juan tiene muchas dificultades delante de él (John has a lot of difficulties in front of him).
Finally, ante means before in the sense of in the presence of:
Lo mandaron comparecer ante el juez (They ordered him to appear before the judge).
One additional note for epistolary or letter-writing usage: Ante todo means before all else or, more commonly in English, first of all.