If I link out to relevant, high quality websites, how many links can I put in percentage? I assume putting a link on every post is a bad idea, but if for every ten posts, there's one outbound link, is it too much?
According to https://yoast.com you need to include an outbound link on every post and the link must me related source. Just make sure the outbound link is nofollow.
I usually put one or two in a post. Not too many though, as that deducts from the link juice that would flow from your post page back into your site, via the internal links in your navigation and on the page.
Imagine for a minute that Google does not exist. How many would you place in each article? a specific number? No, you would place just as many links as the article really needs. That's the way you need to think about it. It could go from zero links to a hundred. It does not matter.
Outbound links only encourage visitors to click away from your site without literally offering them with the needed value. Therefore it helps them, but it's not good for your SEO. An excellent general rule is to work towards including a maximum of five external links for lengthy posts you have on your blog.
Ignore this useless comment. You can make outbound links as much as as you can. Just you have to make them relevant. So that it don't seem that you are selling links somehow. Now that being said. Outbound link means that link juice will be flowing away from your site. And remember a no-follow link doesn't mean that it will stop bleeding link juice from your site. It will flow out your link juice same as a do-follow one. So, for the sake your site you should be very careful where you a put a link.