When to use nofollow links in SEO?

Hello. I have been doing SEO-links for more than a three years, while always choosе certain sites and links that would link to my sites. Also I avoid text links that are non-clickable, in my opinion these links are not useful. Usually I use in my work only dofollow links but I know that nofollow links can play a big role in SEO. I think that Google consider nofollow links too but I don't know how to get right this links for my sites and in which cases it's recommended to use nofollow links, including paid links. Please, answer me, when I should use nofollow links? Thanks.