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.
Read more: Steve Schofield Weblog
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.
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
Look at CPU, Memory and disk counters. Make sure the server has enough resources.
Read more: Steve Schofield Weblog