1. If you are trying to join two different but connected independent clauses, you would use a semicolon.
2. If you are joining two independent clauses where one clause introduces a short list, you would use a colon.
3. If you are joining two independent clauses where the second clause clarifies the first, you would use a colon.
4. You should not use a conjunction after a semicolon that separates two independent clauses; the semicolon itself serves to link the clauses without the need for an additional conjunction.