Most websites will use the http://www.website.com structure as their main website URL and this will be the address used in link building campaigns. However in some circumstances, you may find that Google has indexed two versions of your homepage. E.g.
These are called “canonical” URLs and for the best search engine results, you should get rid of all but one, and stick to it!
Use the Google site command to see if there are any extraneous URLs. Type in site:www.website.com to see what pages are indexed. If you have a large site, also try site:www.website.com/index.html or whatever your “index” page is. If both exist, you should go through your website links and point all your “home” links to just one of them. Also consider putting a 301 redirect on extra pages to the URL that you have been using the most or link building to so that all possible link authority is transferred to the page you have been using for your link building campaign.
If you have several pages that contain largely the same content, e.g. an e-commerce site that has two URLs for one product – where one is navigated through “Brand” and one is navigated through “Style”, the best thing to do is to 301 redirect the best URL through your.htaccess file.
This is the same for the www. vs non-www. issue. As for the the trailing slashes, Google Webmaster Central comforts you with advice that it’s not such a bad thing having URLs with both. This is as long as there is same content on both trailing slash pages and non-trailing slash pages and you are consistent with using the preferred version in internal links, sitemaps and link building from outside links. Google will usually be able to detect the preferred version and rarely will penalise you for this sort of “duplicate” content. However, if you are feeling particularly obsessive about getting rid of the trailing slash for SEO, use a 301 redirect.
Google Webmaster Tools
Use to ‘fetch as Googlebot, currently under “Labs” to see what Google sees and also tell Google your preferred domain.
Google Page Speed
What status server codes does your page return? Downloadable as a Firefox plugin.
Status Server Codes
Is it a 200, 301 or 404? (and what does it mean?)