Let me start by saying that we’re currently developing some very cool tools for Hubs to drive sales to their Hub. Next to that, I know from our most successful Hubs (over 30k in revenue/yr) that they do a lot of ‘old-fashioned’ marketing. Very actively talking to people, going to events, networking etc., in order to get the word out for their Hub. Social Media is also a big help for promoting of course.
It is very effective to put more orders through your Hub as it will earn you reviews which will increase your ranking, which in turn will drive more orders to your Hub. More orders accelerate new orders. Also all our exclusive Hub perks, like filament discounts, are based on the amount of orders a Hub does. So again, running a successful Hub will earn you better deals 
Hope this helps a bit!