I started with Monitoring the application to know what the trending data is for the app to know how to size it. Evaluate what of the services we can be moved to a managed service product or model, reconcile the data layer to see if it is something that we can actually move to the cloud. Once you know enough about your app, then come up with a plan to size, make sure any infrastructure related dependencies are available and ready. If we can create the environment green field and hopefully reproduce the app. If that is not possibly come up with the implementation details to migrate the VM and it's dependencies to its new home.