Before I begin answering this question, let me put forth few definitions.
Cloud is nothing but a bunch of computers at someone else’s place but accessible remotely.
Cloud Computing is basically computing on the computer on the Cloud.
In addition to proving a computer most of the Cloud Service providers have started providing various additional services that makes your life easy. And this comfort is not free. It either comes with strings attached to it so that you can not leave their cloud or it comes at cost.
You should always learn skills that generalization and applicable globally. If you learn the common skills, you will be able to perform better on existing solution as well as on other cloud services.
Such common skills are:
Linux / Unix (Operating Systems)**
Usually when working on a remote computer, you get things done via commands instead of point-and-click using mouse. Commands are very efficient for transmission. A bigger advantage of using commands is that you run bunch of commands in a sequence unattended. This leads to lots of automation. You should know basics of Linux because as of today the server space is dominated by Linux. Here is free tutorial about the same: https://cloudxlab.com/assessment/playlist-intro/2/linux-basics
SQL stands for structured query language. It is kind of query language that helps you process the data in tabular form. It is used in Databases where most of the web applications, mobile applications keep the data. Trust NoSQLs came and went, the databases remained and will remain. The SQL is a huge convenience. SQL is very universal. It can be used to query many systems. Using SQL you can also process big data which is stored on multiple servers by the way of SparkSQL, Hive etc. We created a tutorial on the same: https://cloudxlab.com/assessment/playlist-intro/114/sql-tutorial
When you have to automate or build apps or systems, you need a programming language such as Python. Python is extremely simple to learn. It is also used for a lot of automation on the cloud. You should learn Python. Here is a very hands-on tutorial: https://cloudxlab.com/assessment/playlist-intro/103/python-assessments
Docker has made it really easy to deploy an application. It is really essential to learn Docker in today’s time. Here are some of the resources: https://cloudxlab.com/course/all/?page=1&tag=Docker
Kubernetes and other DevOps tools.
Instead of trying to just cramp-up a particular cloud provider’s services, try learning something that is general such as DevOps. Do take a look at these courses: https://cloudxlab.com/course/60/devops-certification-training
Learn building webapp using Django, Flask, NodeJS before becoming too specific to any platform
Once you have understood these tools, you would ready to handle any Cloud Platform.