How to improve the performance of an ASP.NET application? Which are are the fields I should take care? The application includes DB connections and Image Parsing etc.
try avoiding unnecessary postbacks to pages, there are a lot of features you can implement by using things like jQuery or ExtJs framework. Learn how to do AJAX calls and pass info between your app and the server via JSON result sets.
Also, install apps like FireBug and YSlow and use these to analyze your application and follow their recommendations on how to speed up your app. Good luck!