Pay attention to the following points when you build your URLs:

• Use the page’s keywords in the file name.
• Use only two or three of the page’s keywords in the filename.
• Use-dashes-to-separate-single-words-in-the-file-name (not_with_underscores).
• Make your URLs as short as possible and avoid using any search engine unfriendly characters (e.g. “?&=*#$” or umlauts) in it.
• Define your URL parameters, so Google indexes your website correctly.
• Don’t use too many subfolders in your URL (e.g. http://www.example.com/folder1/subfolder1/subsubfolder1/keyword1-keyword).

Google Webmaster Help: Keep a simple URL structure

Bing Blogs: Search engine friendly URLs