Preassuming that the complexity of your design is fairly average, optimization won't be an easy task. If you are using Synopsis Tools for sythesis and optimization, the book "Advanced Asic Chip Synthesis" Himanshu Bhatnagar Can be helpfull. You can download the e-book in this forum, you need to search.
Optimization of a design is veri skillfull job. Since you haven't mentioned many of the parameters, like complexity, targeting parameters like requency/area and time you have for this activity, it's difficult to comment.