I was recently talking with some good friends about tips for performance and what an IIS Administrator could do on the server side.  I also see this question from time to time in the forums @ http://forums.iis.net.    Of course, you should test individual settings in a controlled environment while performing load testing before just implementing on your production farm. 

• IIS Compression enabled (both static and dynamic if possible, set it to 9)  If you are running IIS 6, check this article out by Scott Forsyth.
• Run FRT for long running pages (Failed Request Tracing)
• Sql Connection pooling in code
• Look at using PAL with performance counters ( http://blogs.iis.net/ganekar/archive/2009/08/12/pal-performance-analyzer-with-iis.aspx ) 
• Look at load testing using visual studio load testing tools
• Log parser finding long running pages.  Here is a couple examples
• Look at CPU, Memory and disk counters.  Make sure the server has enough resources.
• Same machineKey account across all same nodes
• Localize content vs. using UNC based content on a single server (My UNC tag with great posts)
• Content expiration
• ETAG’s the same across all web-farms
• Disable Scalable Networking Pack
• Use YSlow or Developer tools in Chrome to help measure the client experience improvements.

Additionally, some basic counters in for measuring applications is: I would recommend checking out the Chapter 17 in IIS 7 Resource kit. it was one of the chapters I authored. :)

• Concurrent Connections, 
• Request Per / Sec,
• Request Queued. 

I strongly suggest testing one change at a time to see how it helps improve your performance.  Hopefully this post provides a few options to review in your environment.  

Cheers,

Steve Schofield
Microsoft MVP - IIS