Aim for scalable costs
The cloud eliminates the need to overprovision resources, so you should design your workloads to be scalable. This means that you should use the right amount of resources for your current needs, but you should also be able to scale up or down as needed.
Use (only) what you need
Pay-as-you-go is the default pricing model in the cloud, so you should only use the resources that you need. This means that you should carefully size your resources and you should use resource monitoring to track your usage.
Take advantage of reserved instances and other discounts
Azure offers a variety of discounts, such as reserved instances and Azure Hybrid Benefit. You should take advantage of these discounts to reduce your costs.