Once you've created your website and put plenty of good content on your pages, it's time to include both inbound and outbound links. Visitors will leave your website a some point anyway, but outbound links can direct them to high-quality relevant websites that complement your information.
Outbound links can both directly and indirectly influence SEO rankings by affecting your website's reputation. If your website links to bad resources, chances are you'll chase people away from your website pretty quickly, and search engines will punish your website. Engaging in keyword and link spam will only serve to harm your website, putting you at risk of making your website useless.
By linking to high-quality resources that provide good supplemental information without helping competitors, you can boost your website's reputability among both users and search engines. As a result, you can even get more people to supply inbound links to your website, which can help solidify your online presence. People are also more likely to read an entire page of content if it appears well-referenced and heavily researched. While you may want to create a resources page, you can also benefit more often from simply linking to references in context naturally within content throughout the website.
Take the time to test all of your inbound and outbound links as well, using link testing tools, and fixing any that don't link to a page that returns a 200 HTTP code.
Google doesn't provide a specific ratio of inbound to outbound for SEO value because then every spammer would attempt to reach that exact ratio. Generally, you're better off sticking with an even 1:1 ratio of high-quality inbound and outbound links alike, but you should focus more on quality over quantity. However, you should also take into consideration your website's individual goals. For instance, a website that serves as a directory or an encyclopedic source of information will include a large number of links to sources, with likely more outbound than inbound links. On the other hand, an e-commerce website that wants to get people to buy products or services will want to reach as many people as possible with lots of inbound links.
Using high-quality outbound links in conjunction with the rest of your SEO campaign, you can make your website a success that rises and stays well above competitors with inferior tactics.