Use words in URLs - URLs with words that are relevant to your site's content and structure are friendlier for visitors navigating your site. Visitors remember them better and might be more willing to link to them.
• using lengthy URLs with unnecessary parameters and session IDs
• choosing generic page names like "page1.html"
• using excessive keywords like "baseball-cards-baseball-cards-baseballcards.htm".
• Create a simple directory structure - Use a directory structure that organizes your content well and is easy for visitors to know where they're at on your site. Try using your directory structure to indicate the type of content found at that URL.
• having deep nesting of subdirectories like ".../dir1/dir2/dir3/dir4/dir5/dir6/page.html"
• using directory names that have no relation to the content in them
Provide one version of a URL to reach a document - To prevent users from linking to one version of a URL and others linking to a different version (this could split the reputation of that content between the URLs), focus on using and referring to one URL in the structure and internal linking of your pages. If you do find that people are accessing the same content through multiple URLs, setting up a 301 redirect from non-preferred URLs to the dominant URL is a good solution for this.
• having pages from subdomains and the root directory (e.g. "domain.com/page.htm" and "sub.domain.com/page.htm") access the same content
• mixing www. and non-www. versions of URLs in your internal linking structure
• using odd capitalization of URLs (many users expect lower-case URLs and remember them better)