有則改之，無則加勉

correct any mistakes you made, but maintain your good record if you did not make them (idiom)

to have; there is / (bound form) having; with; -ful; -ed; -al (as in 有意[you3 yi4] intentional)

(conjunction used to express contrast with a previous clause) but / then / standard / norm / principle / to imitate / to follow / classifier for written items

(literary) (conjunction used to express contrast with a previous clause) but; then / (bound form) standard; norm / (bound form) principle / (literary) to imitate; to follow / classifier for written items

to change / to alter / to transform / to correct

(possessive particle, literary equivalent of 的[de5]) / him / her / it

not to have / no / none / not / to lack / un- / -less

to add / plus / (used after an adverb such as 不, 大, 稍 etc, and before a disyllabic verb, to indicate that the action of the verb is applied to sth or sb previously mentioned) / to apply (restrictions etc) to (sb) / to give (support, consideration etc) to (sth) / Canada (abbr. for 加拿大[Jia1 na2 da4]) / surname Jia

to exhort / to make an effort