In this article I am going to show how we can set
default focus and default button in asp.net.
For this we need to set property in <form> tag...
like below
<form id="form1"
runat="server" defaultbutton="btnRegister" defaultfocus="txtName">
Output:
When page load then default focus set:

Image 1.
If you press enter then default button is register...

Image 2.
ASPX code is:
<%@ Page Language="C#"
AutoEventWireup="true"
CodeFile="Default.aspx.cs"
Inherits="_Default"
%>
<!DOCTYPE html PUBLIC
"-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<title>Set Default Button & Default Focus in ASP.NET</title>
</head>
<body>
<form id="form1" runat="server"
defaultbutton="btnRegister"
defaultfocus="txtName">
<div>
<table cellpadding="4"
cellspacing="4"
width="70%"
align="center"
style="border: solid 1px Gray;">
<tr>
<td align="right"
width="20%">
Name:
</td>
<td>
<asp:TextBox ID="txtName"
runat="server"
Width="200px"></asp:TextBox>
<asp:RequiredFieldValidator
ID="rfvName"
runat="server"
ControlToValidate="txtName"
ErrorMessage="Enter
Name"></asp:RequiredFieldValidator>
</td>
</tr>
<tr>
<td align="right"
width="20%">
Email:
</td>
<td>
<asp:TextBox ID="txtEmail"
runat="server"
Width="200px"></asp:TextBox>
<asp:RequiredFieldValidator
ID="RequiredFieldValidator1"
runat="server"
ControlToValidate="txtEmail"
ErrorMessage="Enter
Email"></asp:RequiredFieldValidator>
</td>
</tr>
<tr>
<td align="right"
width="20%">
Password:
</td>
<td>
<asp:TextBox ID="txtPassword"
runat="server"
Width="200px"></asp:TextBox>
</td>
</tr>
<tr>
<td align="right"
width="40%">
Mobile:
</td>
<td>
<asp:TextBox ID="txtMobile"
runat="server"
Width="200px"></asp:TextBox>
</td>
</tr>
<tr>
<td>
</td>
<td>
<asp:Button ID="btnRegister"
runat="server"
Text="Register"
Width="140px"
/>
</td>
</tr>
</table>
</div>
</form>
</body>
</html>