Magento – How to prevent magento duplicate meta title and meta description on google webmaster tools

First I would login to the Webmaster Tools with Google and you can specify parameters for it to ignore like you're experiencing with some URLs. Site Configuration -> URL Parameters

I would also make sure you are submitting sitemap.xml properly to Google and other Search engines to help ensure things are crawled properly.

Robots.txt docs:

• https://developers.google.com/webmasters/control-crawl-index/docs/robots_txt

Next I would make sure your robots.txt file is being read and recognized. Here is one I've used with success before:

## robots.txt for Magento Community and Enterprise

## GENERAL SETTINGS

## Enable robots.txt rules for all crawlers
User-agent: *

## Crawl-delay parameter: number of seconds to wait between successive requests to the same server.
## Set a custom crawl rate if you're experiencing traffic problems with your server.
# Crawl-delay: 30

## Magento sitemap: uncomment and replace the URL to your Magento sitemap file
# Sitemap: http://www.example.com/sitemap/sitemap.xml

## DEVELOPMENT RELATED SETTINGS

## Do not crawl development files and folders: CVS, svn directories and dump files
Disallow: CVS
Disallow: .svn
Disallow: .idea
Disallow: .sql
Disallow: .tgz

## GENERAL MAGENTO SETTINGS

## Do not crawl Magento admin page
Disallow: /admin/

## Do not crawl common Magento technical folders
Disallow: /app/
Disallow: /downloader/
Disallow: /errors/
Disallow: /includes/
Disallow: /lib/
Disallow: /pkginfo/
Disallow: /shell/
Disallow: /var/

## Do not crawl common Magento files
Disallow: /api.php
Disallow: /cron.php
Disallow: /cron.sh
Disallow: /error_log
Disallow: /get.php
Disallow: /install.php
Disallow: /LICENSE.html
Disallow: /LICENSE.txt
Disallow: /LICENSE_AFL.txt
Disallow: /README.txt
Disallow: /RELEASE_NOTES.txt

## MAGENTO SEO IMPROVEMENTS

## Do not crawl sub category pages that are sorted or filtered.
Disallow: /*?dir*
Disallow: /*?dir=desc
Disallow: /*?dir=asc
Disallow: /*?limit=all
Disallow: /*?mode*

## Do not crawl 2-nd home page copy (example.com/index.php/). Uncomment it only if you activated Magento SEO URLs.
## Disallow: /index.php/

## Do not crawl links with session IDs
Disallow: /*?SID=

## Do not crawl checkout and user account pages
Disallow: /checkout/
Disallow: /onestepcheckout/
Disallow: /customer/
Disallow: /customer/account/
Disallow: /customer/account/login/

## Do not crawl seach pages and not-SEO optimized catalog links
Disallow: /catalogsearch/
Disallow: /catalog/product_compare/
Disallow: /catalog/category/view/
Disallow: /catalog/product/view/

## SERVER SETTINGS

## Do not crawl common server technical folders and files
Disallow: /cgi-bin/
Disallow: /cleanup.php
Disallow: /apc.php
Disallow: /memcache.php
Disallow: /phpinfo.php

## IMAGE CRAWLERS SETTINGS

## Extra: Uncomment if you do not wish Google and Bing to index your images
# User-agent: Googlebot-Image
# Disallow: /
# User-agent: msnbot-media
# Disallow: /

Source: http://turnkeye.com/blog/optimize-robots-txt-for-magento/

If There is a CMS page then go to the CMS >> Page >> Add/ edit you find the META tab in that you can add Keywords and Description. and title will come form Page Information >> Page Title.

If you load the product then This will load from the Catalog >> Manage Products >> you find in Meta Information Tab in that.

Magento Load this data Dynamically.

Hope you got the Proper Answers.