First. Know your load curves: everything starts from them!
Second. Do not oversize the power of the cogenerator: you could pay for it!
Third. Consider all costs: construction, changes to hydraulic and electrical lines, noise barriers, temporary works: they could make the investment not profitable!
Fourth. Calculate savings with caution: energy taxes could increase dramatically, the value of incentives is very volatile, consider the plant operating costs
Fifth. Really protect you by means of a good contract: guarantee performances, define costs of ordinary and extraordinary maintenance, decide severe penalties for delays and inefficiencies, and do not accept constraints on your future energy consumption.