How to write an asp.net C# code as company expectation or experienced candidate code

Hello Everyone
i have attended the lot of interview and cleared the telephonic round in all the companies but when i am attending the machine test rounds maximum companies are told that you code is very basic level and your code is not like 2+ exp ,but i have complete the task always what they given, in my organization i am only the developer, i dont have existing project in my concern . actually i dont know how to write the code in procedural way for asp.net with C#, is there any format for upgrade my coding ,or is there any links to refer 
this may be help not only for me,this may help many peoples so is there any way to write code typically please let me know

here is my coding 
protected void Page_Load(object sender, EventArgs e) { if (!Page.IsPostBack) { Session.Clear(); Session.Abandon(); } } protected void submit_Click(object sender, EventAr ...