I’ve got by, by thinking external links to other sites should probably be on single pages deeper in your site architecture, with the pages receiving all your Google Juice once it’s been “soaked up” by the higher pages in your site structure (the home page, your category pages). This tactic is old school but I still follow it. I don’t need to think you need to worry about that, too much, in 2019.
Another excellent guide is Google’s “Search Engine Optimization Starter Guide.” This is a free PDF download that covers basic tips that Google provides to its own employees on how to get listed. You’ll find it here. Also well worth checking out is Moz’s “Beginner’s Guide To SEO,” which you’ll find here, and the SEO Success Pyramid from Small Business Search Marketing.