There's no "exact way" - each site deserves a tailor made approach. Still..
1) Shortlist the social media sites where your link targets hang out.
2) Shortlist your link targets
3) Set a time limit for each site ( else it can become time sink )
4) Track your targets using RSS feeds, Yahoo Pipes, Advanced search, lists, etc
5) Engage first. Help their agenda first .Underplay your own pitching.
6) Review your social returns at least once a month.
Funny thing about social sites is that more you use for commercial reasons, more it will erode your influence.
Aim to build quality relationships via social media - links WILL follow.