There are two types of run-on sentences. The first occurs when two main clauses are joined by a comma only. This is called a 'comma splice'. e.g. Meteorology is fascinating to me, I watch the Weather Channel every day.
The second type of run-on sentence occurs when two main clauses have no punctuation separating them. This can occur with or without a conjunction. e.g. Meteorology is fascinating to me I watch the Weather Channel every day. e.g. Meteorology is fascinating to me and I watch the Weather Channel every day.
You can correct a run-on sentence in several ways. The method you choose in correcting your writing will depend on the relationship you want top convey between the two clauses.
One method is to add end punctuation between the clauses and make two sentences. [Meteorology is fascinating to me, I watch the Weather Channel every day.] Another way is to separate the clauses with both a comma and a coordinating conjunction. [Meteorology is fascinating to me, and I watch the Weather Channel every day.]
Alternatively you can add a semicolon and a conjunctive adverb between the clauses. [Meteorology is fascinating to me; I watch the Weather Channel every day.] You can change one of the main clauses to a subordinate clause. Separate the two clauses with a comma if appropriate. [Because meteorology is fascinating to me, I watch the Weather Channel every day.]