There are many verbs that are irregular in the preterite. Their forms must be memorized.

DAR:

di, diste, dio, dimos, disteis, dieron

IR:

fui, fuiste, fue, fuimos, fuisteis, fueron

SER:

fui, fuiste, fue, fuimos, fuisteis, fueron

The rest of the irregular verbs share the preterite endings -e, -iste, -o, -imos, -isteis, -ieron. Notice that none of the endings have accent marks. For these verbs you can learn the irregular preterite stem and use the appropriate endings. NOTE: The third person singular form of hacer has a spelling change of c > z: hizo. Also, the third person plural form of decir and traer does not use the -i- of the ending: dijeron, trajeron.
 

hacer > hic-

estar > estuv-

tener > tuv-

poder > pud-

poner > pus-

querer > quis-

saber > sup-

venir > vin-

decir > dij-

traer > traj-