There is a very comprehensive guide that provide design principles, design
reviews, check lists, how tos and more all for improving the performance of
.NET applications.

http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dnpag/html/scal
enet.asp

Its broken down by activities (design, development, measuring) and
technology (ADO, ASP, SQL, XML, etc).

I would suggest going through the design and code checklists and look for
problem areas. Try to tackle the "low hanging fruit" and schedule the larger
structural changes for the next phase of the project unless you're dead in
the water.

This group has also been responsible for some great security guidance too.

Hope that helps.

====================

eAndy

====================

This might also help:
http://www.aspnetresources.com/articles/debug_code_in_production.aspx
Make sure that inweb.config the compilation node, debug="false" is set.
Many people overlook this setting.

Rudi