In order to be successful in your writing exam you will need to know a variety of tenses, do you know all the preterite tense regular endings for AR/ER/IR verbs.

Verb ending in AR: Nadar (to swim). Before adding on the endings we take off the -ar ending and then depending on who is carrying out the action is the ending we add.
Yo nadé Tu nadaste El/ella/Ud nadó Nosotros nadamos Vosotros nadasteis Ellos/ellas/Uds. nadaron
Verbs ending in IR and ER which have regular endings in the preterite tense both take the same endings. For this example we'll use Comer (to eat). Prior to the conjugation we will take off the -er ending and then we can conjugate accordingly.
Yo comí Tu comiste El/ella/Ud. comió Nosotros comemos Vosotros comisteis Ellos/ellas/Uds. comieron
Examples of commonly used regular preterite verbs: Ayudar, Comer, Comprar, Estudiar, Existir, Hablar, Llamar, Nadar, Pasar, Preparar, Trabajar, Vender, Viajar, Vivir