Undergraduate / English class; MY SECOND LIFE/ Significant Experience [7]

Do not begin the essay with broken sentences or sprinkled nouns. Turn them into a full sentence.

Use past tense in all of the beginning sentences; you are being inconsistent, and present tense does not really serve any purpose.

"Not because..." is a broken sentence. Connect it to the sentence in front of it.

"Not because I really believed what I was thinking" Thinking about what? It's an ambiguous sentence. Clarify "what I was thinking."

"For different people, it can mean different things" is a bad cliche and cluttered sentence. Basically, it does not say anything. The following sentence can be used on its own.

"was very entertaining(it can be tiring as well!)": Do not use exclamation mark. It looks too juvenile on any essay--it's a good thing to remember. Change it to "very entertaining and yet tiring"

"Attending an American high school, with me being a pure foreigner and being there "just for the experience" was an amusement on its own" has a subject agreement problem and is a broken sentence. The subject should be "I," and you should rephrase the whole sentence because it's not clear at all.

"I realized that fun...": Put "such" in front of fun. "I realized that such fun..."

Have comma in front of and after "where I had spent most of my life"

"adjust[ING] to a completely new environment, liv[ING] with strangers, [and missing] my friends and family": Here, you should use gerund form when listing, and "not to add" breaks the uniformity of the list.

Take single quotation mark off from "weird." You should not use quotation marks unless absolutely needed (which means irony, sarcasm, or specifying, not regular emphasis), and even if you use one, it should not be the single quotation mark but double one.

Put comma after "for example."

"I found out that I could do more than I thought I could": So many clutters. Change it to "I could do more than I thought."

"It's true that still I am not the most athletic person one would meet" is a cliche. Change it into something more direct and sincere.

"finishing the season successfully helped me" sounds like "helping" was successful. Or is that what you meant? if not, move "successfully" to the front.

"Experiencing different things, soon, I could see a more confident me": Change to "Experiencing different things, I found a more confident self."

These list may seem a lot and harsh, but believe me. I'm a Korean professional tutor on admission essays, and I taught over 60 students during the past 5 years. :)

But it looks like the old Common App essay topic. Are you using it for the college admission? Cuz this year's topic's different...

Undergraduate / English class; MY SECOND LIFE/ Significant Experience [7]

Your style is largely okay. You seem to have a good sense of writing naturally (i.e. your writing reads naturally when spoken out).

Here are the basic rules:

-4S: Short, Simple, Straightforward, Solid.
The 4S rule applies to all levels of writing: word, sentence, paragraph, and the whole.
Use the shortest and simplest words without losing connotation.
Sentences should be short and simple(without many commas) too if possible, and any meaningless clutter (ones I pointed out in my correction) should be removed, since it lengthens the sentence and obscures the meaning.

A paragraph should contain only one idea. Short paragraphs are better as long as they are made with more than three sentences.
From sentences to paragraphs to the whole essay, everything should flow naturally as one solid piece. You should pay attention to the relationship between two adjacent elements.

-Remove adverbs and adjectives as much as possible, and write with verbs and nouns.
Adverbs and adjectives do not contribute to the style. Use the minimum. Try to find the strongest action verbs and the most colorful nouns possible within your comfortable vocabulary range.

-No exaggeration, no exclamation mark. You don't have to be stoic, but always have control over the expression.

-Use passive only when you are emphasizing something in the subject. Make the sentence active with strong action verb as much as possible.