@Roman123  
I'm sort of a grammar Nazi so all I can offer is grammar and sentence structure corrections.  
  
Para 1:  
Sentence 1: I would leave out bracketed sentence.  
Sentence 2: "Some people consider(believe) that referring (insert 'to') others' opinion(s) before deciding(agreeing) (insert 'on') the decision is an ..."  
  
Sentence 3: "In my view(opinion), I agree with them."  
  
Para 2:  
Sentence 1: "First and ~~the~~ foremost, making others part of (insert 'the'/'your') decision (insert 'makes it') ~~is~~ easy to come ..."  
  
Sentence 3: "Like in (insert 'the') classroom, teachers ~~are~~ (insert 'can')  hardly get  ~~rid~~ (insert 'eliminate') of ~~any~~ (insert 'all their') mistakes, they need our students' notices."(<honestly don't know what 'they need our students' notices' means. would remove)  
  
  
Sentence 5: "...because one individual ~~is impossible to be~~ (insert 'cannot possibly be an') expert in every field ...  
  
Sentence 7: "So referring (insert 'to') others' opinion(s) increases the likelihood ..."  
  
Para 3:  
Sentence 1: "... listening to others' suggestion(s) enhances the whole ..."  
Sentence 3: "Just imagine what  ~~it~~ would happen if the leader is the only one ~~to~~ make(ing) decision(s)."  
  
Sentence 4: "... assignments without any ~~suggestion~~ (insert ' contribution to the project') as well as novelty."(really not sure about 'as well as novelty')  
  
Sentence 6: "Once I was ~~the~~  minster of (insert ' the') secretary department in (insert 'the'/'our') student union."  
Sentence 7: "~~At~~ (insert 'in')the beginning, I only distributed assignment(s) to every member and told them how to ~~do~~ (insert ' complete it')."  
  
Sentence 8: "~~But~~ I found out that they were so ~~inactivity~~  (insert 'inactive') and our tasks were ~~hardly~~ (insert 'barely') approved by teachers."  
  
Sentence 9: "Finally, I changed my  ~~mind~~ (insert 'leadership style') and every time before I made (insert 'my') decision I always ..."  
  
Sentence 10: " Surprisingly, they became more  ~~enthusiasm~~ (insert 'enthusiastic')  than before and ~~give~~ (insert 'contributed') more ideas, meanwhile teachers gave ~~high evaluation~~ (insert 'immense praise) to our work~~s~~."  
  
Sentence 11: "Therefore, taking others' idea(s) is a good way for (insert 'a') leader to enhance the total productivity (insert 'group or organisation')."  
  
Para 4:  
Sentence 1: "~~The~~ last but not ~~the~~  least, an (...) others' suggestion(s) because it (insert 'is') likely to establish a harmonious phenomenon(<not sure about this. maybe try 'experience')."  
  
Sentence 2: "I believe that (insert 'the') leader shouldn't just focus on result, (insert 'but') also (insert 'the') procedure (insert 'as it') is equally important for a team.  
  
Sentence 3: "So a harmonious phenomenon is critical."(<not sure about this)  
Sentence 4: "... communication among leader(s) and members."  
Sentence 5: "Later the team fill with grasp and laughter."(<again not sure. what does grasp mean in this context)  
Sentence 6: "As a consequence, the team(s) relationship ~~gets~~(insert 'becomes') closer and members increase their loyalty to (insert ' the') leader too."  
  
Sentence 7: " ... an aspect to indicate ~~effective~~(insert 'effectiveness')."  
  
Para 5:  
Sentence 1: "To wrap up, allowing others (insert ' to be a') part of the decision making process ~~by leaders~~  contributes to wise decisions as well as (insert 'contributing to the') high productivity of (insert 'the') team also establishes a harmonious phenomenon(<again not sure)."  
  
Sentence 2: "So (insert 'I believe that') leader(s) should try (insert 'implementing) this strategy (insert' in their group or organisation)."  
  
Sentence 3/4: "~~Do you remember the saying?~~(insert 'as the (old)(<optional) saying goes,)  two minds are better than one."