Six design tips for better URLs

It’s an area that is overlooked on many websites, but URL design is an important consideration. Bad URLs may mean that you website won’t be found, visited, or submitted to sites like Digg.
Ideally, URLs should be short, readable, descriptive and memorable. Visitors to your site, other sites linking to yours, and of course the search engines will appreciate the care you have taken over your URL structure.
Here are a few tips for URL design…
Make URLs readable
If your URLs are readable and describe the content of the web page they lead to in some way, people will be more likely to click on them.
For example, this URL from VentureBeat is easy to understand: http://venturebeat.com/2008/09/17/google-to-buy-valve/, but this one from ClickZ is incomprehensible: http://blog.clickz.com/080916-122203.html. There are far worse ones out there too - for some reason, laws of nature and all that, the bigger the media brand the worse this seems to become (serial offenders include CNN, Reuters, MSNBC, etc).
Keep them short
A short URL is more likely to be remembered and is much easier for people to type it straight into the address bar on their browser.
Also, if you need to email a link to someone, a long longer than around 70 characters will not display well in many email clients. Easier said than done, in many cases (it can be tricky for publishers).
Make them permanent
People bookmark webpages on their browsers, or on social sites like Digg, and Delicious so, once you have published a web page, don't alter the URL as users clicking these bookmarked links will just encounter an error.
Make them guessable
If your URL structure makes sense, then people will be able to guess and navigate around a site by editing the URL. For example, if you are on this page: http://econsultancy.com/blog, then you know that, by removing the 'blog' part you can get back to the homepage, or add another term, such as research to reach that section of the site.
Use keywords in URLs
Having keywords in URLs can be useful for search engines, as well as making them more readable. This is something that Google has advised in the past.
Another reason for including keywords is that, as the URL will be displayed under the page title and extract in search results page, this information may be used by people considering whether to click on a link.
Avoid session IDs
As different URLs are generated for different human visitors,  Session IDs cause search robots problems. As a result many search robots have a rule that they don’t crawl these pages since there are many different pages addresses for different sessions.
Websites that have registration processes, or wish to track user activity will often use session IDs; an alternative is to use session cookies instead.