Creating the right structure for your site is very important.  The URL can help a user to understand what to expect on the next page and decide if they want to click on the link.  Google’s Webmaster Guidelines states:

“A site’s URL structure should be as simple as possible. Consider organizing your content so that URLs are constructed logically and in a manner that is most intelligible to humans (when possible, readable words rather than long ID numbers). For example, if you’re searching for information about aviation, a URL like http://en.wikipedia.org/wiki/Aviation will help you decide whether to click that link. A URL like http://www.example.com/index.php?id_sezione=360&sid=3a5ebc944f41daa6f849f730f1, is much less appealing to users.”

This handy guide will help you to decide if you need to consider restructuring your URLs and what your optimised URL structure might look like.

Avoid Connective Words

Words such as ‘and’, ‘or’, ‘but’, ‘a’, etc are not necessary in a URL and unnecessarily extend it’s length. This is not a hard and fast rule, as sometimes it can make sense to add some of these in to help make sense of the page.  My own personal rule is if it’s a category remove all connective words or break into separate categories, if it’s a product limit connective words as much as possible.

Remove Repetition

It can be tempting to repeat keywords in a URL as we often look at the category slug individually when coming up with naming conventions.  However repetitive keywords not only extend the length of a URL they also make your site look spammy.

Example:

BAD:
example.co.uk/long-and-short-sleeved-shirts/long-sleeve-shirts/striped-shirts/large-red-long-sleeved-stiped-shirt-double-cuffed-19845.html
GOOD:
example.co.uk/shirts/long-sleeve/large-red-striped-double-cuffed.html

Simplify Descriptions In URLs

Whilst it is important to have the words that users will be looking for in your URLs it is important not to go to town on this.  Having overly descriptive URLs again will unnecessarily lengthen your URLs but will also make them harder to remember.

Example:

BAD:
example.co.uk/photo-frame/umbra-prisma-photo-frame-5-x-7-13-x-18cm-copper-finnish
GOOD:
example.co.uk/photo-frame/umbra-prism-copper

Ensure Your Landing Pages Are At The Right Depth

Although this might not necessarily effect the length of your URL I think it is worth considering when assessing a site structure.  It’s a common mistake is to bury products in several subcategories, each subcategory presents an opportunity to optimise for different keywords and present to users relevant search results.  However with each new tier in the site structure the authority of the product becomes weakened.  This does depend on the number of products you are selling, with more products you are a more likely to need more subcategories, however remember that no product should be more than 3 clicks from the homepage.  Anything beyond that you risk frustrating and putting off users converting to customers.

Example:

BAD:
example.co.uk/mens/shirts/short-sleeve/t-shirts/polo/large/red.html
GOOD:
example.co.uk/mens/t-shirts/large-red-polo.html

Avoid Product ID’s

Using a product ID can help to create unique URLs, however they offer the user little in the way of expectation from the landing page.  They are also not easy to remember and make it difficult for a user to type the URL directly into the browser to find the product, or recommend to a friend.

For Example:

BAD:
example.co.uk/my-product-19845.html
GOOD:
example.co.uk/my-product.html

Use Separators

You may be forgiven for thinking that by removing spaces between words will save you from having overly long URLs.  However it is much easier to read and interpret a URL when the words used are separated.  But should you use the hyphen (-) or the underscore (_)?  Google’s Webmasters Guidelines are very clear

“We recommend that you use hyphens (-) instead of underscores (_) in your URLs.”

For example:

BAD:
example.co.uk/shortsleeveshirts
example.co.uk/short_sleeve_shirts
GOOD:
example.co.uk/short-sleeve-shirts

TL/DR

When looking at your sites URL structure consider when you could remember, or quickly work out what is on that page just by looking at the URL.  Keep it simple and easy to read will not only please search engines by also, and more importantly, anyone using your site.  Short, user-friendly, URLs will make it easier for other site owners link to you and help to not only build your authority but also bring users onto your site.