News Courtesy of Yoast.com:
Ground rules for SEO-friendly URLs
No matter what kind of website you have, there are a couple of ground rules that apply to all websites.
- The main thing to keep in mind is that your URLs should be focused. Strip your URLs of stop words like ‘a’, ‘of’, ‘the’ etc. In 99% of the cases, these words add nothing of value to your URL. If possible, strip your URLs of verbs as well. Words like ‘are’ or ‘have’ are not needed in your URL to make clear what the page is about.
- The length of your URL isn’t really a factor in this. We do recommend to keep your URLs as short as possible. It’s not that Google doesn’t like lengthy URLs, but shorter URLs are most probably more focused. Keep in mind that if you use breadcrumbs on your site, as we do, these could appear instead of the full URL:
- Length isn’t that much of an issue: Google will show what they think is important for that visitor. Keep in mind that meta titles and descriptions are cut off at 512 pixels, and so is your URL.
- Don’t use underscores, as these connect the words and make them into one. Dashes are preferred.
Ryan’s Take 
The crew at Yoast really don’t want you to use stop words in your URLs. Stop words, like “the”, offer no benefit and are unnecessary. If you look at some of the posts on this blog, they differ in length and do contain various stop words. While I agree that they aren’t going to help increase your rankings for a particular keyword, I don’t believe that they will have a negative impact all that much.
Many people aren’t going to care too much what is in their address bar. What they want is engaging content. I’ve seen plenty of high ranking pages for high volume keywords use the exact title as the URL name. Although you wouldn’t want to have that URL mention a completely different subject, it isn’t something you should be overly concerned with.
What about having a parent category as part of the URL? Is that really necessary? I’d say, only if it makes sense. Your primary focus should be on your visitors and their experience. Let’s say you own a plumbing business and a popular service you offer is for main line drain repair. You might have this service listed under residential services, and then drains, and finally main line drain repair. Should all those keywords be included in the URL for that service? If your website is structured in such a way that many services are broken up into those sections, then yes. However, if we’re only talking about several services, it’s probably not going to matter that much.
