URL structure helps a lot to get your website ranked. Even Google instruct webmasters to give attention to the structure of URL. A good URL always get a better chance to win the ranking game.
What is a good URL structure?
A url that is simple and descriptive is considered good. A good URL create a context and improves the chance of being chosen by the users. A url should be made of readable words rather than numbers, IDs and other non-readable parameters.
Hyphen or Underscore?
You can use the hyphen (-) in the URL but avoid the underscore ( _ ).
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, use readable words rather than long ID numbers in your URLs.Source: Google’s URL Structure Guideline
Human Readable URL Structure
The URL should be human-readable. A user can know the content of the page by reading the URL.
Examples of Good and Bad URL structures
The URL should be enough descriptive to make users click on it even after ranking in the bottom ranks. Higher CTR is an indicator of good URLs.