You have to know Mac OS X, and I don't mean "know how to use Mac OS X." My Mom can use Mac OS X. A good Mac tech needs to understand the fundamental structure of the operating system and how the components relate to each other. For instance, know what Frameworks are and how they differ from Extensions. You should understand the various levels of the operating system, like why there are three "Library" folders or four/five "Fonts" folders. If you're not sure about what's lurking underneath the glossy GUI that Apple gives us, then start investigating. You don't necessarily have to change anything, but it doesn't hurt to look. Start reading some of the excellent tutorials on the Web like those over at kernelthread.com or ArsTechnica You don't necessarily have to understand everything right away. Just immerse yourself in the technology and eventually it'll start making sense.
I don't care if you know how to use Conflict Catcher. Really, I don't. What's that, you say? You know that Suitcase 8 conflicts with the ATM control panel? Good for you. I'm sure that knowledge will we useful here in mid-2006 just like that certificate you got in operating a telegraph machine. I was that guy 10 years ago and I made a good living doing it, but that was the state of tech ten years ago. You don't want to be that guy today. The one exception to this that I'll grant is that there are still a few stubborn holdouts using Macs running System 8 and Mac OS 9. If you're the unlucky soul that has to support these machines [waves at D.C.], then sure, keep that knowledge and use it. But you should probably be preparing yourself for the inevitable switch to Mac OS X (or to Windows, shudder).
Consider Learning Scripting
Some Mac techs are lucky enough to have come from a Unix background and have mastered shell scripting. The best Mac techs I know are scripting wizards and can whip together a script to do almost anything. That is the true power of Mac OS X, you know. Its Unix underpinnings make it versatile, stable, and secure. Buy a good beginning book on shell or Perl scripting and start experimenting. I am certainly not a scripting whizkid, but I've gotten to the point where knowing some scripting is helping to reduce my workload, which is the ultimate goal anyway, right? What's that? You like performing the same identical configuration task on each of 400 Macs?
Use the Resources and Stay Current
The Mac community, and by extension, the Mac technical community, are lively collections of interesting, fascinating, and helpful people. Learn about websites like AFP548.com and MacEnterprise.org. Lurk on some of the better Mac technical mailing lists, even if their subject matter is over your head. I subscribe to half-a-dozen Mac tech mailing lists (such as Mac-Mgrs, MacEnterprise, Mac OS X Server, and Tidbits) and the collected knowledge in their archives is incredible. If you subscribe to a list, just lurk for awhile and follow the list rules. I've found a Gmail account and its handling of email conversations an astonishingly good fit as a mailing list receptacle. Whenever I encounter a new problem, I immediately turn to the mailing list archives (most are online and searchable) to see if anyone else has encountered the problem and whether there's a known solution or workaround. Another sometimes-overlooked but amazing resource are Apple's own discussion forums. The signal-to-noise ratio is quite high, but there are a lot of really smart people answering questions, many of them Apple employees.
Practice keeping documentation of the problems you've solved, or at least bookmarks to sites where you found a solution. I've lost count of the number of times I've solved a problem, didn't document it, and then had to re-solve the problem 2 months later. Documenting your troubleshooting steps and process will also improve your articulation, writing, and communication skills. You don't have to make your documentation public, but many people do. You might even contribute to the mailing lists or websites that I've been talking about in this post, or even to that scrappy little TUAW blog.
Apple's professional certification program has come a long way in the last few years. They now offer several levels of technical certification and a wide range of classes to better your knowledge of Mac OS X and its related technologies. If your goal is to be an attractive candidate for a Mac technical position, having an ACTC or ACSA certification is certainly going to carry more weight than having only Microsoft certs or no certs at all. For awhile, i was teaching some of Apple's courses and know that the team of people they have working on the manuals and course design is very knowledgeable and competent.
Following some of all of this advice will likely get you started on your way to becoming a good Mac tech. There's a lot more that I could put in this post, and I'm sure that some of our readers will have things to add as well in the comments.
Oh yeah, remember my brother Craig who taught himself to be a car mechanic? Last Christmas he bought a computer. He was pretty new to computers so he asked me for help teaching him how to set it up and use it. I tried to explain to him what this whole Internet thing was about and what I do for a living. He looked at me and shook his head, "How on Earth do you know all this!? Jeez!" I smiled and handed him a stack of computer magazines and said, "Start reading."