1) Subject-Verb Agreement

The subject and verb of a sentence must agree with one another in number whether they are singular or plural.

2) Sentence Fragments
Sentence fragments are incomplete sentences that don’t have one independent clause. A fragment may lack a subject, a complete verb, or both.

3) Missing comma after introductory element
A comma should be used after an introductory word, phrase, or clause.

4) Misuse of apostrophe in 'Its'

You use an apostrophe with it’s only when the word means it is or it has. Without the apostrophe, its means belonging to it.

5) No comma in a compound sentence

A comma separates two or more independent clauses in a compound sentence separated by a conjunction. A comma goes after the first clause and before the coordinating conjunction that separates the clauses.

6) Misplaced or Dangling Modifier

A misplaced modifier is a word, phrase, or clause that is improperly separated from the word it modifies or describes. A dangling modifier is a word or phrase that modifies a word not clearly stated in the sentence.

7) Vague Pronoun Reference

When replacing a noun, its antecedent should be the person, place, or thing to which the pronoun refers. A vague pronoun reference (e.g. it, that, this, and which)leaves the reader confused about what or to whom the pronoun refers.

8) Wrong Word Usage

Using incorrect words can change the meaning of the sentence. There are a lot of words/phrases that are often misused in writing.

9) Run-On Sentence

A run-on sentence occurs when you connect two main clauses with no punctuation or connectives.

10) Superfluous Commas

This is when commas are used when they are not required or at all necessary. This is a common writing error.

11) Lack of parallel structure

This occurs when two or more parts of a sentence are similar in meaning but not parallel (or grammatically similar) in form. It often occurs with paired constructions and items in a series.

12) Sentence Sprawl

A sentence can become a burden to read when there are too many equally weighted phrases.

13) Comma Splice

A comma splice occurs when two separate sentences are joined with a comma rather than a period or semicolon. It is common when using transitional words, such as however, therefore or moreover.

14) Colon mistakes

A colon is used after a complete sentence to introduce a word, phrase, clause, list, or quotation. The colon signals that what follows proves or explains the sentence preceding the colon.

15) Split infinitives

An infinitive is the word “to” with a verb. A split infinitive separates the word “to” and the verb with another word (often an adverb). There are no grammar rules that prohibit split infinitives, but many experts disapprove of them.