The next day about 10 o'clock in the morning.

This was a sentence fragment so I added it to the next line to make it complete. A complete sentence needs a subject and a verb. This fragment has no verb.

The next day at about 10 o'clock in the morning, I was already in the downtown areas of SZ.

I could see the Diwang Building (Shun Hing Square) which was the highestallest at over 300m at that time.

The air was fresh and most of the people were in clean dresses whileclothes walking quickly, and the green belt was wide and beautiful...

I had no time to appreciate the scenery because I had no job then and had made no reservation for a single room for me that night.

If I went back to find a job again in an unfamiliar city, I shwould have reserved a room at least.

This is another hypothetical so it's again in subjunctive test. You'll get there!

In order to save time, I went to a career agent asking for the latest job recruitment information, I'll to prove that it was the right decision.

the staff person greeted me without any smile.

I think LangCorrect split the line at the quotation mark so I think you know that this part goes directly after the quotation.

"I want to find a job," I answered timidly."

I answered timidly.

This goes with your quotation.

Our information is updated hourly, t. These are effective immediately and the latest information which is all 100% guaranteed. "," the staff person said quickly while presenting an A4 paper filled with job news.

the staff said quickly and present an A4 paper filled with job news.

"It's 100 yuan per each piece of information, i. If you are failed forfail at the first one, come back and we will give you another two more pieces of information for free.

You also can pay a monthly fee to become oura premium membership... "

I founddiscovered that an exhibition center was recruiting, and their job description stated the following: a university certificate and fluent communicationcy in English were prerequisites; relevant working experience iwas not necessary; a strong desire to develop in a creative field.

I wanted to try getting the job though I haved no university certificate.

I started listening to VOA (vVoice of America) both in English and in Chinese program in 1989. (I was in gGrade 9 then, and 1989 was a special and sometimes sensitive numbeyear in China).

頑張り屋さんですよね。

The next day, at about 10 o'clock in the morning.,

This needs to be joined to the next sentence...

The next day, at about 10 o'clock in the morning, I was already in the downtown areas of SZ.

I could see the Diwang Building (Shun Hing Square) which was the highest -- over 300m at that time.

You need some kind of break between "which was the highest" and "over 300m at that time." I would go for an em-dash (--) but a comma (,) could also work.

The air was fresh and most of the people were in clean dresses whiledressed cleanly and walking quickly, and the green beltgrass was wide and beautiful...

dress -- Dress has multiple related meanings. The most common is an item of women's clothing. Saying people were "in clean dresses" suggests they are all women. I don't think that's what you mean here. Changing this to "dressed well" makes it clear they have any kind of clothing, but clean.

while walking quickly -- This is fine, but "while" is a little odd to use after "were in." Usually it pairs with a more active-sounding verb. ("He was talking while eating")

green belt - I'm not sure what you mean here! It sounds maybe like a section of nature or grass, so I changed it to grass.

I had no time to appreciate the scenery because I had no job then and had made no reservation for a single room for me that night.

Needs the past perfect, since you would have made the reservation before your story began.

It's interesting and a little bit ridiculous becausethat I didn't prepare enough.

If I went back to find a job again in an unfamiliar city, I shwould have reserved a room at least.

(Present/Future) If I go back...., I should ...
(Hypothetical) If I went back...., I would ...

In order to save time, I went to a career agent asking for the latest job recruitment information,. I'll prove that it was the right decision.

tThe staff person greeted me without any smile.

Our information is updated hourly, these are effective andaccurate and have the latest information, which is all 100% guaranteed. "

the staff person said quickly and present aned me a piece of A4 paper filled with job news.

"100 yuan per information, if you are failed forjob lead. If you fail the first one, come back and we will give you another two more pieces of informationleads for free.

"piece of information" is fine, but "job lead" is a more specific phrase for this context.
"are failed for" is also fine, but sounds a little off

You also can pay a monthly fee to becomeget our premium membership... "

GET our premium memberSHIP
or
BECOME a premium member

I found an exhibition center that was recruiting, a. A university certificate and fluent communication in English were prerequisites; relevant working experience iwas not necessary; a strong desire to develop in a creative field was suggested.

"were" is past, so "was" must also be

I wanted to try theo get job though I haved no university certificate.

Stay in past tense (from previous sentence)

I started listening to VOA (vVoice of America) both in English and Chinese program in 1989 (I was in grade 9 then, 1989 was a special and sometimes sensitive number in China).

Were you listening to VOA in both English and Chinese? Or were you listening to VOA in English and also listening to a different program in Chinese? I think you mean the first one, so I dropped the word "program" (which makes it confusing)

The next day about 10 o'clock in the morning.

There is no main verb, so the sentence isn't finished yet.

I could see the Diwang Building (Shun Hing Square) which was the highest over 300m at that time, at over 300m tall.

Or "was the highest at that time, being over 300m tall".

Or "was the highest at that time, being over 300m in height.

The air was fresh and most of the people were in clean dresses while walking quickly, and the green belt of grass was wide and beautiful...

If I say "they were stumbling while walking quickly", it implies they weren't stumbling when they weren't walking quickly.
That implication doesn't work with wearing clothing, because of course they were wearing the same clothing when they slowed down and stopped.

The phrase "green belt" sounds like a belt that a person wears, without some context to suggest that you mean a belt of grass--at least, that is my guess as to what you mean by it here.

I had no time to appreciate the scenery because I had no job then, and had made no reservation for a single room for me that night.

It wasn't grammatically wrong to say "a single room for me that night", but if you just say "a room for that night", it implies that it is single room for you.

It' was interesting and a little bit ridiculous because I didn't prepare enough.

Present tense isn't absolutely wrong, because you could mean that it is interesting and ridiculous for us now thinking about it, but because this is in the middle of a story set in the past, it is jarring to switch to present and then back to past.

If I went back to find a job again in an unfamiliar city, I shwould have reservedreserve a room at least.¶
¶
Or "If I were to go back to find a job again in an unfamiliar city, I would reserve a room at least."

In order to save time, I went to a career agent askingnd asked for the latest job recruitment information,. I'll proveshow that it was the right decision.

Since the natural sequence is that first you went to the agent and then you asked the question, "went and asked" is the natural verb forms here, I believe.

I think "prove" sounds unusual, because you're not talking to a skeptic here.

the staff person greeted me without any smile.

Usually "the staff" refers to multiple people, but as you quote someone, it sounds like you are talking about one person in particular.

Our information is updated hourly, these are effective and the latest information, which is all 100% guaranteed. "

the staff person said quickly, and presented an A4 paper filled with job news.

or "the staff worker" or even just "the worker", or "the placement person"

"100 yuan per information,opening, and if you are failrejected for the first one, come back and we will give you another two more pieces of informationopportunities for free.

We could talk about "a job opening" or "an opening" or "an opportunity" or "a job opportunity" or "an advertised job"

You also can pay a monthly fee to become oura premium membership... "

Or "to join our premium members"
or "to receive a premium membership"

I found an exhibition center was recruiting, at which a university certificate and fluent communication in English were prerequisites; relevant working experience iwas not necessary;, but just a strong desire to develop in a creative field.

I wanted to try for the job even though I haved no university certificate.

I started listening to VOA (voice of America) both in English and Chinese program in 1989 (I was in grade 9 then, 1989 was a special and sometimes sensitive numbeyear in China).

Or "I started listening to VOA..., both the English and Chinese programs, in 1989..."

I assume you mean the year 1989. We never really speak of a year as a number.