If you are using an Exadata system, the same rules apply:
you still need to provide the Optimizer with accurate information on the data you are accessing and the system you are running on so it can determine the optimal execution plans. In order to ensure that the Optimizer is fully aware of the performance that your Exadata system is capable of, you should gather system statistics in your environment using the new Exadata option. This will allow the Optimizer to fully understand the performance capabilities of the Exadata environment. Other than that you should operate just as you do on any other platform. Oracle will automatically take advantage of the Exadata features for each of the operations in the execution plan that will benefit from them.