Example sentence + explanation:
The ship returned to port. Its propeller was broken.
The information in each independent clause is considered important. However, in reality, the first clause is more important. It is more important to know that the ship had to return to port, then that the propeller is broken.
Why? The company (owner) needs to know that their cargo was returned and not delivered.
They may have to make arrangements quickly, or they might lose money.
To let the reader know which clause is more important, you can make one of the independent clauses into a dependent clause by adding a subordinating conjunction to the front of the clause.