Let's create a new module with a module declaration file:
app/etc/modules/Shashank_Adminhtml.xml
<?xml version="1.0"?>
<config>
<modules>
<Shashank_Adminhtml>
<active>true</active>
<codePool>local</codePool>
<depends>
<Mage_Adminhtml/>
</depends>
</Shashank_Adminhtml>
</modules>
</config>
Create your module directory structure and a config.xml:
app/code/local/Shashank/Adminhtml/etc/config.xml
<?xml version="1.0"?>
<config>
</config>
We need to rewrite a block inside the admin panel, so let's turn on template hints in the admin. In our config.xml:
<?xml version="1.0"?>
<config>
<stores>
<admin>
<dev>
<debug>
<template_hints>1</template_hints>
<template_hints_blocks>1</template_hints_blocks>
</debug>
</dev>
</admin>
</stores>
</config>
The grid container we want to override is: Shashank_Adminhtml_Block_Catalog_Product_Grid
Let's rewrite our block with the rewrite node inside our config.xml:
<?xml version="1.0"?>
<config>
<global>
<blocks>
<adminhtml>
<rewrite>
<catalog_product_grid>Shashank_Adminhtml_Block_Catalog_Product_Grid</catalog_product_grid>
</rewrite>
</adminhtml>
</blocks>
</global>
<stores>
<admin>
<dev>
<debug>
<template_hints>1</template_hints>
<template_hints_blocks>1</template_hints_blocks>
</debug>
</dev>
</admin>
</stores>
</config>
Let's create a class that rewrites that block. We will use: Shashank_Adminhtml_Block_Catalog_Product_Grid
.
<?php
class Shashank_Adminhtml_Block_Catalog_Product_Grid
extends Mage_Adminhtml_Block_Catalog_Product_Grid {
}
Now, with our template hints still on, let's check to see that it's being rewritten.

Now, all we have to do is set our default sort attributes and default filters. We will do that in the __construct()
method of our class.
<?php
class Shashank_Adminhtml_Block_Catalog_Product_Grid
extends Mage_Adminhtml_Block_Catalog_Product_Grid {
public function __construct() {
parent::__construct();
$this->setDefaultSort('type');
$this->setDefaultFilter(array('type' => 'configurable'));
}
}
Now, turn off the template hints and see that it's being rewritten.

I hope this helps.