I am not an expert, but I think blog commenting, forum posting, e-mail marketing, social media.. That is what I use for my blog, and will go on using for my future forum ( made with
https://www.templatemonster.com/bbpress-wordpress-themes.php ). I want to try guest posting, but have no single idea what to start with.
This method I think is already outdated. Only social media sites like facebook, youtube or twitter is the best method to advertise your website and you can even target specifics audience on those social media sites I mentioned.
I agree with you - on social networks you can very quickly promote the site. There are even special pages where you can post links to your site for free. And there are programs that send out spam and make publications for the target audience