I modified the file – catalog/controller/product/product.php.
I found out the line in this file-
$this->document->setTitle($product_info['name']);
Modified it as-
$this->document->setTitle("Buy " . $product_info['name'] . " in India");
Similarly, I modified the next line, which was originally-
$this->document->setDescription($product_info['meta_description']);
As-
$this->document->setDescription("Buy " . $product_info['name'] . " in India at an affordable price. Information, Specifications & Reviews for " . $product_info['name']);
Similarly you can perform this action for the home page, the categories and other taxonomies. For categories modify this file – catalog/controller/product/category.php.