P.T. Barnum was a great American Showman in the 19th century. Below is a summary from his 1880 book, Golden Rules for Making Money. There are 20 rules in all. Sure, you will have read similar advice before, but remember, this was written before any of the modern self-help books were written. You can read the whole book chapter-wise online.

1. Don't mistake your vacation: Unless a man enters upon the vocation intended for him by nature, and best suited to his peculiar genius, he cannot succeed.
2. Select the right location.
3. Avoid debt.
4. Persevere.
5. Whatever you do, do it with all your might.
6. Depend upon your personal exertions.
7. Use the best tools.
8. Don't get above your business: There is no greater mistake than when a young man believes he will succeed with borrowed money. Without self-denial and economy, patience and perseverance, and commencing with capital, which you have not earned, you are not sure to succeed in accumulating.
9. Learn something useful.
10. Let hope predominate but be not too visionary.
11. Do not scatter your powers.
12. Be systematic.
13. Read the newspapers.
14. Beware of "Outside Operations" (read the chapter online to learn more about this)
15. Don't indorse without security.
16. Advertise your business.
17. Be polite and kind to your customers.
18. Be charitable.
19. Don't blab: Some men have a foolish habit of telling their business secrets.[this is my favorite]
20. Preserve your integrity.

[From the 100 Ways To Be Being Remarkable Series, a special project that brings you business and self-development advice from The Success Manual. ]