Library Works, a website devoted to "helping libraries prosper," has compiled a list of best practices on a wide variety of topics. If you'd like some insight into things such as library design, shelving, book repair, low cost teen areas, what to look for in a reading chair (and much more), visit their Best Practices page.
Another great resource is Library Success: A Best Practices Wiki. Again, it is a compilation of a variety of best practices, as experienced by libraries around North America (primarily the US).
Categories include: Management and Leadership, Materials Selection, Readers' Advisory, Reference Services and Information Literacy, Selling your Library/Marketing, and Services to Specific Groups.