To be honest, this is a general question, and the answer can be different for each industry. I mean if you are an agency that offers services on retention basis, a viral blog post or one good speaking gig at a known conference can give you enough leads to lifting your revenue up to 35−40%, but if you are in fashion retail, things will be very different.
One thing we did for a client to increase their income to a real extent was ‘product review'. We find the top journalists and bloggers and contact them for product reviews (we also used HARO for this) and once we get the reply we give them a choice to pick their favourite products and review them accordingly.
We aren’t ideally looking for links but the quick buzz that result in a significant improvement in revenue. We managed to get mentions in magazines like Huffington Post and Buzz Feed, which lead to a huge bump in traffic and sales. But, these authority links significantly improve rankings as well, which help us get most targeted traffic and revenue against our core terms on a regular basis.