I have written 14 best practices here, read them all and let me know what is as per your opinion should be the 15th best practice.
1. Store relevant and necessary information in the database instead of application structure or array.
2. Use normalized tables in the database. Small multiple tables are usually better than one large table.
3. If you use any enumerated field create look up for it in the database itself to maintain database integrity.
4. Keep primary key of lesser chars or integer. It is easier to process small width keys.
5. Store image paths or URLs in database instead of images. It has less overhead.
6. Use proper database types for the fields. If StartDate is database filed use datetime as datatypes instead of VARCHAR(20).
7. Specify column names instead of using * in SELECT statement.
8. Use LIKE clause properly. If you are looking for exact match use “=” instead.
9. Write SQL keyword in capital letters for readability purpose.
10. Using JOIN is better for performance then using sub queries or nested queries.
11. Use stored procedures. They are faster and help in maintainability as well security of the database.
12. Use comments for readability as well guidelines for next developer who comes to modify the same code. Proper documentation of application will also aid help too.
13. Proper indexing will improve the speed of operations in the database.
14. Make sure to test it any of the database programming as well administrative changes.
Let me know what should be the 15th best practice.
Reference : Pinal Dave (http://blog.SQLAuthority.com)