Irregular verbs have their own spellings in present and past tense, which you just have to memorize (since there's no one, overall spelling rule to which they conform). These are some common irregular verbs:
Present
Past
be (am, are)
become
bring
come
do
eat
get
hear
know
read
say
see
send
take
wear
write
was, were
became
brought
came
did
ate
got
heard
knew
read
said
saw
sent
took
wore
wrote