A comma splice occurs when you attempt to join two sentences with a comma.
The play was incredible, I never wanted it to end.
It's tempting to string a bunch of sentences together with commas because it mirrors the way we speak—and we speak quickly. But two full sentences can never be joined with a comma. Like, ever.
Fixing comma splices
1. Combine ideas.
The play was so incredible that I never wanted it to end.
Remove the comma and combine the two sentences into one. The end.
2. Use a comma and a conjunction.
The play was incredible, and I never wanted it to end.
Add that coordinating conjunction and, and you're good to go. You still need the comma since the two parts of the sentence are both independent clauses. Looks good, doesn't it?
3. Use a semi-colon.
The play was incredible; I never wanted it to end.
Here, we used a semi-colon to link the two sentences about the incredible play because both of the sentences are closely related in content.
4. Use a period.
The play was incredible. I never wanted it to end.
Perhaps the simplest way to correct a run-on sentence is two separate its ideas into two distinct sentences. Easy, right?