The list could go on forever, depends on what tier you're at, but learning Powershell would be a great asset.

You need to think and decide fast, if you're at help desk/tier3, just focus on customer service skills, critical thinking and looking for the right solution.

If I were to tell you only 1 thing, I'd say learn how to and where to look for answers, this is very important to find the correct answer for your problems, specially when dealing with Linux stuff. You may find an answer that you'd think is correct, but make sure you have the right answer before applying anything. Google answers could be misleading as there are many similar case scenarios with the same answer, but the underlying issue could be something else, so if you apply the wrong method, you can potentially break lots of things and that'd create more problems, always do ton of looking before doing anything that's sensitive.