Linking internal posts
Linking internal posts which have some worth reading content is good seo because this way you can make it a major posts and also make it visible on google serps. You can occasionally link to related posts and this way you wont have to buy external links nor be under concern of black hat seo. I have tried this and have seen some posts ranking consistently for several months on google without spending a penny or any other external effort than occasionally linking it from my posts on and off.