My father likes collecting quotes that inspire people to live a positive life. He has saved more than one thousand quotes. Let me share two of them, which my father tells us over and over again.

When you are learning something, don't compare yourself to others. Just compare yourself today with how you were yesterday.

This can also apply to seeing other people's lives on social media. It's easy to compare their highlights with your life, but you don't know the full picture of other people.

When you hear someone saying they wants to die.Please suggest hi, tell them not to die until this time next year. As time goes by, everything will change. Time is people's strongest companion. Many things will happen during this year, and they will make life a huge difference.

If you don't know the gender of the person, it's best to use an inclusive pronoun, they. I also added commas to break up the run-on sentences.

My father likes collecting quotes that inspire people to live a positive life. He has saved more than one thousand quotes. Let me share two of them which fthat her tellold us over and over again.

Changed to make more conversational.

When you are learning something, don't compare yourself to others. Just compare yourself today with how you were yesterday.

Need to add spaces between punctuation

WhenIf you hear someone saying he wants to die.P, please suggest him not toe don't die until this time next year. As time goes by, everything will change. Time is peoplone's strongest companion. Many things will happen during this year and they will make life a huge difference. in life.

My father likes collecting/ taking down quotes that inspire people to live a positive life. He has saved/ taken down/ kept/ remembered more than one thousand quotes. Let me share two of them whichthat my father would tell us over and over again.

some alternative expressions and slight grammar change

When you are learning something, don't compare yourself to others. Just compare yourself today with how you were yesterday.

today is fine, but i wont think i would use it in this sentence as it's implied it's today.

When you hear someone saying he wants to die.P, please suggestell/ encourage/ comfort him not to die until this time next year. As time goes by, everything/ many things will change. Time is peoplea person's strongest companion. Many things will happen during this year and they will make lif(add up and) make a huge difference.

"suggest" sounds a bit too formal and shallow when it comes to talking about "wanting to die". Perhaps something more affectionate like my examples. Some extra expressions that could make it sound richer.

My father likes collecting quotes that inspire people to live a positive life. He has saved more than one thousand quotes. Let me share two of them, which fFather tells us over and over again.

You can reword "quotes that inspire people" as "inspirational quotes"
Another way of phrasing "over and over again" is "repeatedly", which you can use to prevent your sentences from becoming wordy.

When you are learning something, don't compare yourself to others. Just compare yourself today with how you were yesterday.

When you hear someone saying that they wants to die.P, please suggestadvise him not to die until this time next year. As time goes by, everything will change. Time is people's strongest companion. Many things will happen during this year and theythat will make life a huge difference in life.

If you don't know the gender of someone, usually you would refer to that stranger as "they", until you know more details.
Perhaps "improve" would fit this context better than "change"?
Instead of "people's strongest companion" you could say "one's strongest companion", which has a formal and literary connotation to it, or "our strongest companion", which is inclusive and more precise.