Is there a guideline or site in where I can information about best practices for configuring IIS 7 Application Pools?
Take a look at http://technet.microsoft.com/en-us/library/cc753734(WS.10).aspx for an IIS 7 overview but look at the Understanding Sites, Applications and Virtual Directories section http://learn.iis.net/page.aspx/150/understanding-sites-applications-and-virtual-directories-on-iis-7/
Hard to really put together best practices since each setup is different, however it usually comes down to performance vs security.
The short answer there is to group similar security requirements into the same app pools but don't be afraid to make additional app pools.