As soon as: "en cuanto"
To say an event will happen as soon as another one does, use the phrase en cuanto. When the action you are waiting for hasn't happened yet, the verb immediately following en cuanto must be in the Present Subjunctive.
The main action—what will happen as a result—can be a command, the simple present (often used for the near future), or a future tense like ir a + infinitive.
| Don't speak as soon as the theatre curtain goes up. | No hables en cuanto suba el telón. |
| The technician has said that we start as soon as he arrives. | El técnico ha dicho que empezamos en cuanto llegue. |
As soon as: "tan pronto como"
Another phrase that means "as soon as" is tan pronto como. It is used exactly like en cuanto and follows the same rule: when referring to a pending future action, the verb following it must be in the Present Subjunctive.
| We are going to need makeup and lighting as soon as the actress arrives. | Vamos a necesitar maquillaje e iluminación tan pronto como llegue la actriz. |
| We put on the music as soon as the boss gives the warning. | Ponemos la música tan pronto como la jefa dé el aviso. |
Word order
The "as soon as" clause can come at the end of the sentence or at the beginning. If it comes at the beginning, use a comma to separate it from the main clause.
| We are going to prepare the set as soon as you finish the makeup. | Vamos a preparar el decorado tan pronto como termines el maquillaje. |
| As soon as the actresses leave the dressing room, everyone to their position. | Tan pronto como las actrices salgan del camerino, todo el mundo a su posición. |
| Change the set as soon as the theatre curtain comes down. | Cambia el decorado en cuanto baje el telón. |