Two common phrases that are taught early on are 잘 지내세요 and 어떻게 지내세요 - as well as variations on each of those.
However, 잘 지내세요 and others can actually sound awkward in many situations. One of the most common places they can sound awkward is when used to strangers. This is because these phrases actually mean "How are you?" and are used when you actually want to ask someone how they're doing. They're not used as casual ways to say "Hello" to strangers you meet.
This is not to say that 잘 지내세요 isn't used commonly, or that it's an awkward phrase. But it's important to know when and how to use it, in order to avoid sounding awkward in Korean.