How do I improve ASP.NET MVC application performance?

A compiled list of possible sources of improvement are below:

General

• Make use of a profiler to discover memory leaks and performance problems in your application. personally I suggest dotTrace
• Run your site in Release mode, not Debug mode, when in production, and also during performance profiling. Release mode is much faster. Debug mode can hide performance problems in your own code.

Caching

• Use CompiledQuery.Compile()
  recursively avoiding
  recompilation of your query
  expressions
• Cache not-prone-to-change
  content using OutputCacheAttribute
  to save unnecessary and action
  executions
• Use cookies for frequently accessed non sensitive information
• Utilize ETags and expiration – Write your custom ActionResult methods if necessary
• Consider using the RouteName to organize your routes and then use it to generate
  your links, and try not to use the expression tree based ActionLink method.
• Consider implementing a route resolution caching strategy
• Put repetitive code inside your PartialViews, avoid render it xxxx times: if you
  end up calling the same partial 300 times in the same view, probably there is something
  wrong with that. Explanation And Benchmarks

Routing

• Use Url.RouteUrl("User", new { username = "joeuser" }) to specify routes. ASP.NET MVC Perfomance by Rudi Benkovic

• Cache route resolving using this helper UrlHelperCached ASP.NET MVC Perfomance by Rudi Benkovic

Security

• Use Forms Authentication, Keep your frequently accessed sensitive data in the
  authentication ticket

DAL

• When accessing data via LINQ rely on IQueryable
• Leverage the Repository pattern
• Profile your queries i.e. Uber Profiler
• Consider second level cache for your queries and add them an scope and a timeout i.e. NHibernate Second Cache

Load balancing

• Utilize reverse proxies, to spread the client load across your app instance. (Stack Overflow uses HAProxy (MSDN).

• Use Asynchronous Controllers to implement actions that depend on external resources processing.

Client side

• Optimize your client side, use a tool like YSlow for
  suggestions to improve performance
• Use AJAX to update components of your UI, avoid a whole page update when possible.
• Consider implement a pub-sub architecture -i.e. Comet- for content delivery against
  reload based in timeouts.
• Move charting and graph generation logic to the client side if possible. Graph generation
  is a expensive activity. Deferring to the client side your server from an
  unnecessary burden, and allows you to work with graphs locally without make a new
  request (i.e. Flex charting, jqbargraph, MoreJqueryCharts).
• Use CDN’s for scripts and media content to improve loading on the client side (i.e. Google CDN)
• Minify –Compile– your JavaScript in order to improve your script size
• Keep cookie size small, since cookies are sent to the server on every request.
• Consider using DNS and Link Prefetching when possible.

Global configuration

• If you use Razor, add the following code in your global.asax.cs, by default, Asp.Net MVC renders with an aspx engine and a razor engine. This only uses the RazorViewEngine.

  ViewEngines.Engines.Clear();
ViewEngines.Engines.Add(new RazorViewEngine());

• Add gzip (HTTP compression) and static cache (images, css, …) in your web.config
  <system.webServer>
<urlCompression doDynamicCompression="true" doStaticCompression="true" dynamicCompressionBeforeCache="true"/>
</system.webServer>

• Remove unused HTTP Modules
• Flush your HTML as soon as it is generated (in your web.config) and disable viewstate if you are not using it
  <pages buffer="true" enableViewState="false">