Should I put my main keyword on every page, including blog posts?
The short answer is no. When you optimise every page and post for the one thing, other than it looking truly awful and spammy to users, you risk losing control of which page or post is shown. I've seen many examples of this where clients have followed inaccurate advice from 'SEO Courses' or well-intentioned Facebook groups, and the result has been a blog post from 2012 has been page 1 for [insert city] 'wedding photographer' instead of their homepage. I am then hired to fix this type of hot mess, so as much as this is great for my business ;-) it's pretty awful for yours, and anyone who is advising you to spread your main keyword throughout your website like that simply does not understand how SEO works. To be totally clear on this, it's not that this information is simply out of date, it's always been a bad idea.