20 ways to increase the selling power of copy

From Tested Advertising Methods (John Caples and Fred E. Hahn), ch. 11

1. Use present tense, second person
2. Use subheads
3. Put captions under illustrations
4. Use a simple style of writing (KISS for SUCCSES)
5. Choose simple (short) words
6. Give free information
7. Use selling copy, not style copy
8. Arouse curiosity
9. Make your copy specific
10. Use long copy (in direct mail letters)
11. Write more Copy than is necessary to fill the space (it trims down nicely during editing)
12. Avoid helping your competitors (highlight unique features)
13. Use mail order methods in direct mail advertising
14. Understatement versus overstatement
15. Avoid trick (untrue) slogans, headlines
16. Get help from others (and always show them TWO headlines/pieces of copy—will make them criticize one of them).
17. Do not say that salesperson will call (even if they will)
18. Study the selling copy in mail order catalogs
19. Make every advertisement a complete sales talk
20. URGE THE READER TO ACT!!