As a rule of thumb, the easier a link is to obtain, the less value it will have; so put the groundwork in. The majority of people won’t link to you just because you ask them. You have to give them something in return that’s of value to them. The most tried and tested method for this is guest blogging. This deserves a whole article in itself, so instead take a look at the work of top SEO professionals like Neil Patel and Matthew Woodward.