A common mistake most English language learners make is forming run-on sentences. A run-on sentence is a sentence in which one or more independent clauses (sentences that can stand as full sentences) are joined together without the help of suitable connecting words, phrases or punctuation. Such sentences are not only ungrammatical but they also prevent the reader from receiving the intended meaning of the writer. A run-on sentence may result from simply the omission of punctuation marks:
Run-on: "I went to school in Ankara it is the capital of Turkey."
Correct: "I went to school in Ankara. It is the capital of Turkey."
However, sometimes mistakes are not as simple as left out punctuation marks. There may be more global grammar errors such as omission of connecting words, relative pronouns, main verbs and detection of such errors requires careful editing on part of the writer.
Run-on: "Mr. Baker used to teach arts in Memorial High School I used to be a student there."
Correct: "Mr. Baker used to teach arts in memorial High School, where I used to be a student."
As ESL students start making longer and more complex sentences, run-on sentences occur more often. The remedy is editing carefully, identifying main verbs and main subjects in independent clauses.