So, I'm basically still a beginner (less than six months) and a late bloomer on top of it (43 years old). As get more involved I'm discovering most of my influences (80s punk and 90s alternative) use alternate tunings, drop D appears to be the most common. My question is what should my competency level be before I start exploring other tunings? I get that everyone is different, but I'm guessing there is some level of core knowledge I should have before branching out?
You'll want to understand what you're tuning to and why rather than just following a tuner.

What I mean is you'll want to be able to find notes on the fretboard. There is a sharp/flat between every note except for between E and F as well as B and C. Understanding this makes things less confusing if you're dealing with just about anything to do with pitch. Also, the way people tune their guitars isn't arbitrary. There's usually something specific people are trying to achieve with different tunings, and trying to get a sense of what that is can help you play easier and sound better. Sometimes you can tell a lot about a band simply by what their guitars are tuned to- tunings can even help define entire genres.

Also, it's a really good idea for any guitarist to learn how to set up their own guitars. You shouldn't have to worry about this for drop D, but if you were tuning further down you would have to adjust some things on your guitar. Sooner or later it's going to come in handy to know how to tweak things, so this is a good skill to have. Once you figure it out, you can even set someone else's guitar up for some beer or something!
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