Typically, there is an inordinate amount of focus on production spends but a lot of that spend (in some cases, more than production) is on dev and test. It is surprising how many times you find unused instances adding to your bills. This usually happens when someone provisions an instance to conduct an experiment or check out a new feature and then fails to delete the instance, when done. It also happens a lot during testing when the test environment is, carelessly, left running through the weekend, or after the testing activity has been completed. It is important to check your bills and usage data to minimize such costs. Tag your instances with environment name, owner’s name, and so on to identify the instances and the primary owner or cost center quickly.

Instances are disposable on the cloud, and they can be switched on and off, easily, so ensure that you switch off your dev, test, and training instances after office hours and through the holidays and weekends. There are several ways to achieve this including scripts, starting up based on time or on request, scheduled auto scaling groups, and so on. On cloud, instances are billed for usage; hence, you do not need to keep them on when they are not being used. You can easily save 30-40% or higher on your bills this way. 

Furthermore, you can leverage AWS Lambda to get rid of idle time on servers. AWS Lambda comes with automatic provisioning and scaling, and there is no need to manage any infrastructure. Typically, if your server utilization is less than 40%, then consider using AWS Lambda instead.