The principles of risk management have been introduced in grid computing to help document and anticipate certain risks and manage them to ensure job executions are successful. Clouds are more complex environments with further concerns like risk, trust, eco-efficiency, green, security or cost. In this paper we present ongoing research work to analyze and address the risk factor in clouds with the aim of optimizing cloud services. The main contribution of this work is the presentation of a methodology for performing risk assessment in cloud environments including the target use cases, risk identification, mitigation and monitoring. Together with the corresponding mitigation strategies, the methodology provides technological assurance that will lead to a high confidence of Cloud service consumers on one side, and a cost effective and reliable productivity of cloud Service/Infrastructure Providers on the other side. The design of the risk assessment framework and its software toolkit implementation are part of the research and development work of the OPTIMIS (Optimized Infrastructure Services) project whose objective is to enable an open and dependable Cloud Service Ecosystem that delivers IT services that are adaptable, reliable, auditable and sustainable both ecologically and economically. The paper presents some preliminary results on the risk assessment of a Service/Infrastructure Provider at the cloud service deployment stage.