One basic way to fix a run-on sentence is to separate the two clauses into two separate sentences with a period. Complete sentences are known as independent clauses. You have a run-on sentence if two have two independent clauses without punctuation, with incorrect punctuation or joined by a conjunction. For example, “It was a hot day, I wore shorts” is a run-on of the two sentences “It was a hot day” and “I wore shorts.” Fix this by writing “It was hot day. I wore shorts.” Notice the period separating the two independent clauses.
Sometimes writing two separate sentences divided by a period is too choppy for the reader. Another way to fix a run-on sentence but keep some flow to the words is to combine the sentences using a conjunction. Conjunctions are the words “and,” “but,” “so,” “or,” “yet,” “for” and “nor.” To fix the run-on sentence, “I love watching television, I couldn't decide what to watch,” write “I love watching television, but I couldn’t decide what to watch.” In the latter sentence, there is the conjunction “but” following a comma. If you combine two sentences with a conjunction, you must write a comma after the first independent clause.
A semicolon links two independent clauses that are directly related to one another. For example, “John loved to travel he decided to go to Europe” is a run-on. To fix this sentence, write “John loved to travel; he decided to go to Europe.” Semicolons are often followed by words such as “however,” “therefore,” “furthermore,” or “nevertheless.” In the sentence above, another possibility is to write “John loved to travel; therefore, he decided to go to Europe.” If you use one of the connecting words, you must write a comma after the word. You can also use an em-dash (a long dash, which is not just a hyphen) to separate the two sentences. When using an em dash, remember that the two independent clauses must be related to one another.
Economy of expression is an important idea when doing any kind of writing; you don't want to say in several words what you can say in a few words. Pretend that you have to pay five dollars for every word that you write and you will get rid of excessive wordiness. Another way to correct run-on sentences is to reduce the two independent clauses into one simpler statement. For example, “The dogs were playing they frolicked in the yard” is a run-on. Write “The playing dogs frolicked in the yard” to fix the run-on.
Words such as “which,” “that,” “who” and “unless” are dependent words that can be used to correct run-on sentences. For example, the sentence “These are the organic apples she bought them at the farmer’s market” is a run-on. Write “These are the organic apples that she bought at the farmer’s market.” You have to get rid of some words in the second clause to make this kind of combination work (the word “them” was deleted from the corrected sentence).