After you have finished writing, click on the headings to see my advice on how to identify and remove various common writing errrors. If you prefer to see all items and explanations in one view, open the long version here.

I. Run-ons
Is there a period (full-stop) at the end of each and every sentence in your essay? If you find that you are using comma after comma, there may be a problem.
..sample error
*Academic writings employ a large number of gerunds and abstract noun phrases, therefore, the subject and verb in a sentence often take the form of complex noun phrases.
...sample solution
Academic writings employ a large number of gerunds and abstract noun phrases. Therefore, the subject and object in a sentence often take the form of complex noun phrases.

II. Two Modals
Are you using double modals, e.g. may, can, will etc., in a clause / sentence? If you are, make sure you remove one of them.
..sample error
*Do you will submit your assignment before the deadline tomorrow?
...sample solution
Will you submit your assignment before the deadline tomorrow?

III. -s / -ed
Do you end your verbs with an "s" or "ed" even when they are immediately preceded by a modal? e.g. can helps, will plans, must visited, should revised. If you do, make sure you omit the "s" or "ed/d". Or you can consider removing the modal.
..sample error
*Student must finished their assignment before the deadline on Monday if they do not want to lose 10% of the course marks.
...sample solution
Student must finish their assignment before the deadline on Monday if they do not want to lose 10% of the course marks.

IV. Connectives
Are you using quite a few connectives? e.g. on the contrary, on the other hand, other than that, besides, as a result. If you are, are you perfectly sure you are using them correctly? If you are not, either just get rid of them or replace them with something easier.
..sample error I
*Fathers are usually strict to children. On the contrary, mothers are often very kind.
...sample solution
Fathers are usually strict to children. In contrast, mothers are often very kind.
..sample error II
*Society should not treat homosexual people unfairly because they were born that way. On the other hand, the government should not take away their right to marriage.
...sample solution
Society should not treat homosexual people unfairly because they were born that way. For the same reason, the government should not take away their right to marriage.

V. Double Verbs
Are you using two fully inflected verbs in one single clause? If you are, change one of the verbs into the -ing form. Alternatively, you can expand the clause to include a subordinate clause in it.
..sample error
*Students attend classes in this period should be optional because they have completed all the assignments and have fulfilled the attendance requirement.
...sample solution
Whether students attend classes in this period should be optional because they have completed all the assignments and have fulfilled the attendance requirement.

VI. There is / are
Avoid using the "there is/are" structure if there is already a fully inflected verb in your clause/ sentence.
..sample error
*There was a university student commit suicide recently because of study pressure.
...sample solution
A university student commmitted suicide recently because of study pressure.

VII. Active / passive
Check your verbs to see if they are used in the correct verb form. For example, "will finished" is not a correct verb form. Check the passive forms to see if they consist of any version of "be + past participle". e.g. "is/are/was/were/is being/are being/was being/will be/would be/has been/have been/had been finished"
..sample error I
*Many students can identified all the errors in the paragraph within five minutes.
...sample solution
Many students can identify all the errors in the paragraph within five minutes.
..sample error II
*All the errors were identify by Peter in less than three minutes.
...sample solution
All the errors were identified by Peter in less than three minutes.

VIII. Subject verb agreement
When writing, you should pay attention to whether your subjects agree with your verbs at all times, especially when using the present tense. That is, when the subject is singular, the verb in the sentence should also be singular. When the subject is plural, the verb should also be plural.
..sample error I
*The quality of the arguments are not good enough.
...sample solution
The quality of the arguments is not good enough.
..sample error II
*It is not easy to decide which one of the three choices A, B, or C answer the question best.
...sample solution
It is not easy to decide which one of the three choices A, B, or C answers the question best.

IX. Count and uncount nouns
When a noun is countable, it may be used in the singular or plural form. If it is used in the singular form, there is usually an article such as "a", "an", or "the" before it. If it is used in the plural form, it usually ends in -s or -es. When a noun is uncountable, "a" and "an" cannot be placed before it, and it usually does not end in -s or -es.
..sample error I
*Researches show that politics has a divisive effect on people.
...sample solution
Research shows that politics has a divisive effect on people.
..sample error II
*In particular, study have shown that men often dominate discussion in which both sex are involved.
...sample solution
In particular, studies have shown that men often dominate discussions in which both sexes are involved.