there is lot of factors to check before replying to such questions.
but in first look, it seems that you already had good content because with just 6 DR, you are doing pretty well and traffic value is also very high with this low traffic, this sign that you are on good cpc money making niche.
So my suggestion to you is get high quality links like niche edits and guest posts (make sure it is niche relevant) and links are not coming from link farm sites. and I am sure you will get good boost.
one more point, choose keywords which are ranking on bottom of first page or 2nd page, so you can boost them on top which will help in increasing your traffic.