The Developer Zone

Disable Session State

Disable Session state for sites that do not make use of it. The performance improvement may be very minimum, but cutting down extra processing for every request is always good. Session state can be disabled in the web.config file:

Session state can also be disabled on individual pages by modifying the "EnableSessionState"
page directive on each page.

Use Output Buffering

By default its enabled. ASP.Net sends response to IIS in a 31 KB buffer, which is then passed to the client. When buffering is disabled, ASP.NET only sends few characters to IIS, thus not utilizing this buffer. Which in turn increases the trips between IIS and the worker process.
To enable it you can change the web.config or you can enable it on each page through @page directive

Avoid Server-Side Validation

Whereever you can use client-side validation instead of Server-Side validation. This will save you from additional reposts to the server in cases of invalid input.

Use Repeater Control And Avoid DataList, DataGrid, and DataView controls

Take advantage of HttpResponse.IsClientConnected, before performing a large operation

The IsClientConnected property returns True if the client is still connected to the Web server during the processing of a response.

Use HTTPServerUtility.Transfer instead of Response.Redirect

Instead of using Response.Redirect, use HTTPServerUtility.Transfer where ever you can. Response.Redirect sends response to the client which then sends a new request to the server. HTTPServerUtility.Transfer however performs the redirect on the server. Only use Response.Redirect when you want authentication and authorization to be performed on redirects or you want URL on client browser to be changed because HTTPServerUtility.Transfer will not do this as it is a server side transfer.

Always check Page.IsValid when using Validator Controls

If you don’t trust the browsers that they will be able to perform complex validations you can still use client-side validation and on repost check Page.IsValid to check if the input passed the given set of rules.

Deploy with Release Build

Win32 Debug :
Full symbolic debugging information is stored in Microsoft format
No optimization

Win32 Release :
No symbolic debugging information is stored in Microsoft format
Optimized for maximum speed

Turn off Tracing

It is important to turn off tracing before deploying application to production. Tracing adds additional overload to your application which is not required in production environment. You can disable tracing in the web.config:

Use Page.IsPostBack

Avoid Exceptions

Managing exception can make development work very easy if used efficiently. However, inappropriate handling of exceptions can degrade the performance of your ASP.Net application.

Use Caching

Caching in ASP.NET dramatically help in boosting application performance by reducing the load on the underlying server by serving cached content that doesn’t need to be recreated on each request. ASP.NET provides two types of caching:

Output Cache: -

which stores dynamic pages and user controls. One each request code is not executed if a cached version of page or control is available

Data Cache: -

which allows application to save application objects, DataSet etc in server memory so they are not recreated on each request. Use caching whenever possible to reduce the load on your web server and to increase response time.

Create Per-Request Cache

In ASP.NET, per-request caching can be done by making use of HttpContext.Items property for data storage. HttpContext is a class that ASP.NET uses for the life cycle of a request/response. For example, when you make a call to Response.Write, you're actually calling HttpContext.Current.Response.Write.

Use of StringBuilder Class for String Manipulation

Turn Off ViewState for controls where Viewstate is not necessary

Avoid using viewstate for storing large objects.Disable it when you don’t need it. ViewState is used by the ASP.Net server controls so that they can retain their state after postback. ASP.NET serializes all objects,controls in the viewstate and transmits them in a hidden field to the client browser. If it is not managed properly, viewstate can increase page size which in result increases network traffic. Also precious CPU cycles are used for serialization, deserialization of viewstate objects.You can disable viewstate if:

Use Paging

When ever using data grid to show data with paging enabled one thing needs to understood that if your query returned let say 1000 record and you are only showing 100 records per page the rest of the 900 record will be discarding and the same will apply when ever you will change the page or apply sorting. The additional 900 rows will definitely take up memory and if your database is located on a different server which is most commonly the case you will also be transferring unnecessary data over the network. Make sure you are only returning the required results to the ASP.NET application by filtering out the data in your database query and apply custom paging. SQL Server 2005 and onwards provide valuable function for ranking data that can be used to accomplish this task.

Use the AppOffline.htm when updating binaries (Applicable Only .Net Framework 2.0 and above)

Use ControlState and not ViewState for Controls

Use the Finally Method

Use Option Strict and Option Explicit