曾经 + Verb + 过 (פעם / בעבר)

A classmate used to live in Shanghai

• I / me我wǒonce曾经céngjīngto live住zhùat / in在zàiShanghai municipality…上海shàng hǎi。 — “I once lived in Shanghai.” The classmate points to an earlier part of their life.
• Compare I / me我wǒnext year明年míng niánto go去qùShanghai municipality…上海shàng hǎi。 — “I will go to Shanghai next year.” A future plan is different from an earlier experience or state.

Place once曾经céngjīng before the past predicate

• Use subject + once曾经céngjīng + predicate: I / me我wǒonce曾经céngjīngto live住zhùat / in在zàiShanghai municipality…上海shàng hǎi / she / her她tāonce曾经céngjīngdegree / adjective linker很hěnshy害羞hài xiū。 The predicate can describe a past activity or state.
• once曾经céngjīng does not require (experience)过guo after every predicate. she / her她tāonce曾经céngjīngdegree / adjective linker很hěnshy害羞hài xiū is a complete past-state example without it.

he他tāonce曾经céngjīngwork as当dāng(experience)过guoteacher老师lǎoshī。

Use (experience)过guo to mark an experience when appropriate

• he他tāonce曾经céngjīngwork as当dāng(experience)过guoteacher老师lǎoshī。 means “He once worked as a teacher.” Here (experience)过guo follows work as当dāng and marks experience.
• I / me我wǒonce曾经céngjīngto go去qù(experience)过guoShanghai municipality…上海shàng hǎi。 reports having been to Shanghai. “Once” in this translation need not mean exactly one visit; state to go去qù(experience)过guoonce; one time一次yī cì if that exact count matters.

Distinguish an earlier state from an exact count

• I / me我wǒonce曾经céngjīngat / in在zàiShanghai municipality…上海shàng hǎito work工作gōng zuò(experience)过guo says the work belongs to an earlier experience. I / me我wǒonly只zhǐto go去qù(experience)过guoonce; one time一次yī cì says the number of visits was one.
• once曾经céngjīng alone supplies neither an exact date nor a count. Add those details when they are relevant instead of inferring them from the English word “once.”

Read later clauses for the present situation

• she / her她tāonce曾经céngjīngdegree / adjective linker很hěnshy害羞hài xiū，now现在xiàn zàican / be able to能néngto have confidence in…自信zì xìn(adverb -ly)地delecture演讲yǎn jiǎng。 explicitly contrasts earlier shyness with the present ability to speak confidently.
• Without a present clause, do not invent every detail of the person’s current life. The earlier-state framing does not establish their current address, job or exact feelings.

Choose a past example and keep its limits

• For a former role, he他tāonce曾经céngjīngwork as当dāng(experience)过guoteacher老师lǎoshī is suitable. For an earlier state, she / her她tāonce曾经céngjīngdegree / adjective linker很hěnshy害羞hài xiū is suitable without (experience)过guo.
• In a new account, identify the past predicate, whether an experience marker fits, and any explicit count or present contrast. Do not add those facts yourself.

Read the full reference: HSK 5 grammar — Adverbs.