Hope you have read how to identify URL parameters for exclusion through Google Webmasters Tool. Now let us see how to do it.
1) Log into your webmasters tool
2) Under Configurations , click URL Parameters
3) If at least a few parameters need attention then you will see a message like – Help Google crawl your site more efficiently by indicating how we should handle parameters in your URL
4) Under Crawl column, you will see two values - Let Googlebot decide and Representative URL. The default value is ‘let Googlebot decide’
5) The representative URLs are picked by Google algorithm based on the crawling history, 301 redirects and rel=”canonical” tag.
6) The common parameter seen in most websites is the ‘sort’ parameter. The webmaster must decide whether the sort just reorders and doesn’t impact the content (read this article)
7) When you edit the parameter, you will get two options:
a) No: Doesn’t affect page content
b) Yes: Changes, reorders or narrows page content
8) Pick the option according to your website
9) There are parameters that will be indexed even after you set directives in robots.txt due to social signals. For such parameters, you can add them manually for exclusion.
A common example is the sessionid parameter
For detailed guidelines watch the following video or read the summary