How to apply “white-list” input validation to protect agains

Question

Hello friend
 
can you tell me proper way to fix Cross Site Scripting (XSS).
 
Description:
XSS flaws occur whenever an application takes un-trusted data and sends it to a web 
browser without proper validation and escaping. XSS allows attackers to execute scripts 
in the victim?s browser which can hijack user sessions, deface web sites, redirect the 
user to malicious sites or possibly introduce worms, etc.
 
By using white-list i able to fixes.But i cant get a proper way.
So can you tell me how to apply 
 
"white-list" input validation to protect against XSS.