Social bookmarking is all about contributing and building into a community before taking out. The goal of this exercise is to join and explore the three social-bookmarking sites and then meaningfully contribute to one and earn a reputation as a value creator. This will pay off down the road, when you start sharing your own more promotion-oriented content.
What happens if you don’t invest the time up front?
You could get banned from the community for sharing too many promotional links or messages. In which social-bookmarking community do you see the most potential? Become a valued member and it could provide an enormous amount of traffic and awareness.