Run-on Sentence

Your typical run-on sentence is an example of commas being used to join sentences.  This is how you can splice wires:

 A comma is a separating punctuation mark.  You cannot use it to splice sentences.  You may use it to set off the end of the first of two main clauses in a compound sentence.  This is how you join sentences.

1.  Coordinate conjunctions join main clauses in compound sentences: and, but, for, or, nor, yet, so.  In the past, and still today, you may see a semi-colon set off the first sentence.

 •••••Jane likes salad with her sandwich, and John prefers soup.  Jane would make a big salad, but John would not eat it.  She makes both salad and soup, for John is hard to please.  She can do this extra work, or she can risk his wrath.  She loves John, yet she is getting weary.  She makes soup and serves it with a smile, so John does not complain.

    In years past 'so' would be considered an adverb, and it would be preceded by a semicolon.   But many people are using it the way it is given above.  When in doubt, see if you should put 'that' in.  If you mean 'so that', you have a complex sentence.   Then, as it would be an adverb clause in the adverb position, it does not require a comma.  This reason is being subordinated to the main clause.
•••••She makes soup and serves it with a smile so that John does not complain.

2.  Semi-colons and colons join main clauses in compound sentences.  They make you slow down at the end of the first sentence, and then let you proceed to the next one.

 •••••Jane makes soup and serves it with a smile; thus, John does not complain.
••••• Jane makes soup and serves it with a smile; therefore, John thinks her well-trained.
••••• Jane makes soup and serves it with a smile; she is serving him arsenic, too. 

3.   An idea subordinated into an adverb clause or an adjective clause or a noun clause does not have to be set off by a comma unless it is out of its normal place.
 •••••Jane likes salad with her sandwich while John prefers soup.  Jane would make a big salad except that John would not eat it.  She makes both salad and soup as John is hard to please.  She must do this extra work unless she would risk his wrath.  She loves John although she is getting weary.  She makes soup and serves it with a smile since John does not have much time left to complain.

Please let me know what else you want to know.