Hey there! I'm happy to help!
The regular form of the imperfect tense for -ar verbs in Spanish is ending the verb with aba (and conjugating). Hablaba, soplababan, pensabas, etc.
For -er and -ir verbs, use ia (my computer can't type accents, but it should still make sense; sorry about that!). Comia, escribian, dormias, etc.
The irregular ones are the ones that don't follow these words. The irregular verbs are normally words like ser, estar, and ir.
I'll list all of the imperfect verbs down below and explain which one is which. Be sure to underline the regular ones and circle the irregular ones on your assignment.
Viviamos- this is regular as it comes from the -ir verb vivir and uses ia.
mandaban- this is regular as it comes from the -ar verb mandar and uses aba.
dar- this is regular because it comes from the -ar verb dar and uses aba.
compraba- this is regular because it comes from the -ar verb comprar and uses aba.
eran- this is irregular because it comes from the -er verb ser and doesn't ia.
saliamos- this is regular because it comes from the -ir verb salir and uses ia.
recorriamos- this is regular because it comes from the -ir verb recorrer and uses ia.
me gustaban- this is regular because it comes from the -ar verb gustarse and uses aba.
era- this is irregular because it comes from the -er verb ser and doesn't ia.
habia- this is regular because it comes from the -er verb haber and uses ia.
iba- this is irregular because it comes from the verb ir and doesn't use ia.
pasabamos- this is regular because it comes from the -ar verb pasar and uses aba.
veiamos- this is irregular because it comes from ver and is veia when it should be via.
escondia- this is regular because it comes the the -er verb esconder and uses ia.
volviamos- this is regular because it comes from the -er verb volver and uses ia.
Have a wonderful day and keep on learning! :D