Randfish of SEOMoz has a blog post consisting 11 guidelines or best practices for successful URLs. As the blog implies, these points are based from an SEO perspective although they are also beneficial for commoun uses too.

1. Describe your content. Because URLs also get pasted, shared, emailed, written down and recognized by search engines.
2. Keep it short. Shorter URLs prevent typos. They are also easier to remember.
3. Static is the way & the light. Some search engines treat static URLs differently than dynamic ones.
4. Descriptives are better than numbers. Words are better than numbers.
5. Keywords never hurt. If you can get every competitive advantage, why not.
6. Subdomains aren’t the answer. Subdomains can be treated separately from the primary domain.
7. Fewer folders. Avoid excesive folders.
8. Hyphens separate best. Hyphens are the separator for words, just like spaces. The next best things are underscores (_), pluses (+) and nothing.
9. Stick with conventions. Let users grasp how you organize folders and pages.
10. Don’t be case sensitive. Make them all lower case.
11. Don’t append extraneous data. This could potentially confuse users and search engine spiders.

For bloggers, these could be used as guidelines when customizing permalink is possible. Some content management software also allows configuration of the URL. Yet, on some sites I decide to go the simple way. For instance, on one of my site that uses Drupal, I decided to stay with /node/<number>, which is very simple and neat.

WordPress blog users are able to customize the permalink to the level where they could follow the domain name immediately with the title as the “file” part of the URL or permalink. This sometimes creates a lengthy permalink. For best example, look at this blog. I purposely include nothing in the permalink structure other than the title of the blog post, separated by hyphens.

Bloggers.com automatically truncates URLs. In this case, it is probably not possible to have keyword rich URLs unless the keywords are at the beginning of the title.

Nowadays, there are rare cases where you have to pass URLs without users capability to click on the link. Most emails support that feature. If you really want to shorten URLs, there are a lot of services out there. You can even setup your own script that also functions to track activities.

Again, don’t sweat though if you can’t comply with any of these. They are nice to have but not by any means compulsory. Even from SEO perspective, getting the perfect URL only benefit your search engine ranking a bit, perhaps negligible.

[SEOMoz]