(1) Think of strating niche specific pinterest profile only. Dont combine two niche on your pinterest profiles unless they are somewhere relevant to each other.
(2) Rule of Thumb - Conside Pinterest as search engine like Google.
(3) Find all sub niches of your main niche and make them seperate boards.
For ex - your main niche is internet marketing so your sub niche would be PPC, SMO, SEO, Content Marketing, Email Marketing etc
In this way I still kept my profile very targeted because when it will send traffic to my money site it will be very targeted.
(4) start adding useful pins to your subniche boards shared by other peoples.
But here is the twist. Most of the pinners dont use proper description to their pins. So while saving their pins to your boards just edit the description and add your own description. You should add your main keyword and few relevant/popular hash tags in description. You can even put your own websites link in description.
(5) Follow industry experts and people who are hyper active in your niche. Regularly comment on their pins which will give you chance to notice by them. If they notice your response and follow you back it would be great.
(6) Now most important getting invites to popular group boards in your niche.
If you have got accepted in group board with 50,000 followers it will be traffic generating machine for your money site.
http://pingroupie.com/ (This is my pro tip)
Pingroupie is the service where you can find the group boards by searching for particular keyword/niche. So with this service you will be able to find niche targeted group boards
(7) Sort group boards results retrieved by pingroupie by number of followers and open their group boards page. If that specific board accepts other contributors into the board there must be instructions written in the description box of group board.
Follow them carefully. Contact admin by following their terms and you will get accepted to those group boards.
Thats it from my side. I have used many other blackhat ways too but I dont want to discuss them here. I will be glad if this adds even minute information to your knowledge.