Best practices in developing ASP.NET applications...

Remove unused  private  fields and functions. Do not cast unnecessarily. Avoid duplicate casts where possible, since there is a cost associated with them. Properties that return arrays are prone to code inefficiencies. Consider using a collection or making this a method. To test for empty  string s, check if  String.Length  is equal to zero. Constructs such as "".Equals(someString)  and  String.Empty.Equals(someString)  are less efficient than testing the  string length. Replace these with checks for  someString.Length == 0 . Methods in the same type that differ only by return type can be difficult for developers and tools to properly recognize. When extending a type, be sure not to define new methods that differ from base type methods only by type. Use  stringbuilder  instead of  string  types for  string  manipulation.  Use  String.Format  instead of concatenating and appending  string s. Use  Type.TryParse  rather than  Convert.ToDestinationType() . For example, use  int.TryParse()  rather than  Convert.ToInt32()  which might throw an exception. Override  Equals()  method wherever applicable in your classes. Consider passing base types as parameters - Using base types as parameters to methods improves re-use of these methods if you only use methods & properties from the parameter's base class. E.g. use  Stream  instead of FileStream  as a parameter when only calling  Stream.Read() , this makes the method work on all kind of  stream s instead of just File streams. Do not catch general exception types - You should not catch  Exception  or  SystemException . Catching generic exception types can hide run-time problems from the library user, and can complicate debugging. You should catch only those exceptions that you can handle gracefully. Use properties instead of visible instance fields. Follow the same naming conventions accross the solution.  Remove unwanted commented code, indent code properly. Use curly braces with in an  if  statement, even if there is a single statement in the  if  block. This will provide better readability. Make sure to refactor your code to move the duplicated code to common reusable functions. Move one time control settings into the .aspx page rather than having them in the code behind in  if(!IsPostback) block. Use inheritance wherever possible, which enables code reuse and also reduces the amount of code we have to write and test. Move the reusable JavaScript functions to an external .js file instead of having them on the page. For controls that are declaratively specified on the page, tie the event handlers to the controls events on the aspx page rather than initializing them in the codebehind. If the controls are built dynamically, then we do not have a choice. Make sure to check for  null s when using any type retrieved from a session, querystring or a database to avoid NullReferenceExceptions . Use  foreach  loop instead of using  for  loop which may lead to out of boundary run time exceptions.