I am assuming that you would know the terms used in
SEO field, hence I will start with a casual talk.
Well, the link building strategy does not work if you have a poor On-page SEO setup! You gotta get your Onpage better before you think about offpage submissions i.e. link building.
1. Target high Domain Authority sites!
2. Search for websites that give you lesser bounce rate and the other websites which give you greater engagement time!
3. See google analytics daily to see which site gives you traffic. Accordingly plan your link building strategy.
Again I must say that there are few agencies which will do SEO wrongly! It is not needed to be aggressive, but calculative! You do not have to do many submissions.