How to optimize an URL?
Several axes of optimizations must be taken into account when choosing a URL.
First of all, it is often about the first contact with your website. Directly from the results page of a search engine, the user will identify a title, a short description, as well as a URL. He will use these 3 criteria, among others, to know whether he will visit your website or not.
Your URL must therefore prompt to click.
By the way, sponsored links professionals providers have known this a long time ago and that is why they optimize this parameter a lot.
In order to be displayed integrally, your URL must be short. It should contain less than 90 characters, ideally 65. It is useless to stuff your URL with keywords and might even be counterproductive or assimilated to spam by Google.
It should consistently reflect the tree structure of your website in order to give the first indications which are sometimes useful.
Being able to read some keywords in your URL is much more intuitive and comforting for Internet users than a series of exotic characters or mostly discouraging numbers (beware of internal references). Furthermore, search engines take into account (slightly) the keywords of the URL as a standard for ranking.
Your URL should use words separated by hyphens (a character located under the button 6 of your keyboard) and every other kind of separator. Not only this will make reading easier but you will also make sure that search engines will get to distinguish each word independently.
Feel free to delete stop words, that is the empty and common words in a specific language because they, sometimes, unnecessarily extend the URLs . In French language for example, words such as « le », « la », « les » et « l' » are referred to as "empty words". These stop words extend therefore unnecessarily the URLs, so it's better to choose "full words" over them.
According to Google, it is often more interesting to include synonyms of the keyword you want to target rather than trying to fit it at all costs.