Example 1
Juan went to the mall he bought new sneakers.
If this fused sentence is any indication, Juan must've been in a huge hurry. But this sentence is a mess. Here's one way to fix it: Juan went to the mall and bought new sneakers. By combining ideas, we can get rid of the run-on, and make this sentence much easier to understand. (And don't put a comma in there—you don't need it. "Bought new sneakers" is a fragment, so it doesn't earn a comma.)