How to bBalance wWork and lLeisure

Most words in titles have a capital letter except joining words like 'to/and' :)

It is vital things for in our life that we have work and leisure,. But wehat should do whatwe to balance work and leisure?

I would try different word orders for this 'Work and leisure are vital things in our lives. But what should we do to balance them?' :)

Work is the foundation thing for our life,. So I choose work between work and leisure,i. If workload is seldom,W we can finish our work within the stipulated time, then relax ourselves.

Stipulated is not a common word. You can also say 'specified', 'alloted' or 'scheduled'.
Also, new point = new sentence.

Of course,If if the workload is very large, we can break it up legitimatereasonably before the deadline.

'Legitimately' is used more often to mean 'lawfully' or an exagerrated 'really' (For example, 'They entered the country legitimately' or 'I legitimately thought I was going to fall asleep') :)

Everyday do some work , then use the time remaining to relax ourselves.

'Relax ourselves' sounds odd to English speakers. Normally we just say 'to relax' :)

We can't just do work without leisure, our body can't supply,cope. At the same time, we can't justhave leisure without doing work.

In English 'work' and 'do work' can mean the same thing.
'Supply' sounds odd, 'cope' makes more sense in the context here.
'Leisure' is usually paired with have, or we use the phrase 'to have leisure time'. You could also replace 'leisure' in your original sentence with 'relax' :)

Therefore, plan thening your time reasonably is very important.

Hopefully we can become a better personople.

Saying 'Hopefully we can become a better person' makes it sound like you are one person. People makes it plural :)

It is vital things for our life thatn our life we need both work and leisure,B but wehat should do whatwe do to balance work and leisurethem?

A phrase is not capitalized after a comma, like this. Only after a period does a new phrase start with a capital letter.

For solving this problem, I have some ideas.

Of course, the pronoun "I" is always capitalized.

Work is foundation thing for oura necessity in life, Sso I choose work between work and leisure,if workload is seldom,We can finish our work within the stipulate time,then relax ourselvesusually one should choose work over leisure. If one has a light workload and can meet all of the deadlines, then one can relax.

If this is general advice, use 'one.'
If this is how you approach deciding whether to work or relax, use 'I' like so:
"Work is a necessity in life, so usually I choose work over leisure. If I have a light workload and can meet my deadlines, then I can relax."

Of course,If if one's workload is very large,wheavy, one can break it up legitimately beforeinto smaller steps to meet the deadline.

In American English, our work duties are usually described as 'light' or 'heavy.'

Alternative: "Of course, if my workload is very heavy, I break it up into smaller steps to meet the deadline.

Everyday do some work ,then the time remaining to relax ourselvesone does some of the work, then one can relax the rest of the time.

Alternative: "Everyday I do some of the work, then I relax the rest of the time."

We can't just do work without leisure, our body can't supply,some time for leisure. At the same time, we can't justalways spend our time in leisure without doing any work.

Not sure what the phrase "our body can't supply" means in your original sentence. Here's my best guess:
"We can't do work without some time for leisure, because it would exhaust our bodies."

TheyBoth are very necessary forital to us.

Therefore, plan thening one's time reasonably is very important.

Alternatives:
"Therefore, one must plan one's time well."
"Therefore, I am careful about planning my time."

Hope we canBy doing this, one hopes to become a better person.

Alternative:
"By doing this, I hope to become a better person."

Check out the verb 'aspire' as used here:
"By doing this, one can aspire to be a better person."