The first step in ROI or ROAS (return on ad spend) optimization is to define the ROI goal. It will become abundantly clear which terms are ROI profitable versus which are ROI negative. Subsequently, as optimizers, we can try to make ROI negative terms profitable and if unsuccessful remove them. With an ROI goal set, we can manage individual keywords, keyword clusters, and the entire account to a goal ROI using basic logic.
http://searchengineland.com/cpa-vs-roi-optimization-what%E2%80%99s-the-best-practice-38818
SEO Monopoly is one of the latest most talked about forms of SEO.