Choosing Colons and Semicolons

For semicolon and colon, I have found out that if in two independent clauses the second one explains the first clause, we use colon; if not, semicolon. How do I know the second case?

My examples:

• Spain is a beautiful country; the beaches are warm, sandy and clean.
• He got what he worked for: he really earned that promotion.

Can I see better examples of sentences with independent clauses?