The Cloud Computing model leverages virtualization of computing resources allowing customers to provision resources on-demand on a pay-as-you-go basis. During recent years, the power consumption of datacenters in cloud environment attracted researchers. Optimization of energy consumption can be performed by different methods including virtual machine (VM) consolidation. This technique can reduce energy consumption by preventing of wasting them. Also, VM migration can provide opportunity to reduce energy consumption. In this article, we want to study dif-ferent methods and policies to select and place VMs and migration algorithms for underutilized and over-utilized servers in order to reduce energy consumption and SLA violation. We offer general and comprehensive framework on optimization of VM consolidation as its owchart and at last, suggest combined idea to detect underloaded and overloaded hosts and also VM selection and VM placement policies.