Your site URLs are like the bridges between your website and a search engine’s crawler: crawlers need to be able to find and cross those bridges (i.e., find and crawl your URLs) in order to get to your site’s content. If your URLs are complicated or repetative, crawlers are going to spend time tracing and retracing their steps; if your URLs are organized and lead directly to distinct content, crawlers can spend their time accessing your content rather than crawling through empty pages, or crawling the same content over and over via different URLs.

Remove user-specific details from URLs.
Remove any URL parameters that change the content of the page—like session IDs or sort order from the URL and put into a cookie.

Disallow actions which Googlebot can’t perform.

If you are using your robots.txt file, you can disallow crawling of login pages, contact forms, shopping carts, and other pages whose sole function is to disallow a crawler from indexing.

With one URL, keep one set of content.
In an ideal world, there’s a one-to-one pairing between URL and content: each URL leads to a unique piece of content, and each piece of content can only be accessed via one URL. The closer you can get to this ideal, the more streamlined your site will be for crawling and indexing. If your CMS or current site setup makes this difficult, you can use the rel=canonical element to indicate the preferred URL for a particular piece of content.