Yes, saying "how's life going?" can be an acceptable way to greet someone, even if it's the first time you're meeting them. It's a friendly and casual greeting that shows you are interested in the other person and their well-being.
Using this kind of greeting can create a relaxed and open atmosphere, making it easier for the conversation to flow naturally. It also allows the other person to share a bit about themselves and how they are doing, which can lead to further discussion and help you get to know each other better.
However, keep in mind that the appropriateness of this greeting may depend on the context and the relationship you have with the person. If you are in a formal or professional setting, you might want to use a more standard greeting such as "Hello, nice to meet you" or "Hi, how are you?" But in most casual or social situations, "how's life going?" is generally well-received.
Ultimately, the key is to be genuine and considerate when greeting someone for the first time, and to be attentive to their response to gauge if they are comfortable with the level of familiarity in your greeting.