As much as big studios with big tape machines have started to go the way of the dinosaur and get replaced by kids with laptops, there's still lots of reasons to acquaint yourself with the techniques used in those situations. One of the most important experiences in my life was learning to record on two and four track reel-to-reel machines. The lessons about gain stages and saturation were priceless and stay with me to this day.
Instead of going into a whole bunch of lessons about what to do in a given situation I'm going to leave that to the fine folks at DPA Microphones who have created Microphone University which of course features their own line of mics but is highly informative, especially on the subject of stereo micing in the studio. (I'll put the link on the Resources page as well.) What I'm going to concentrate on is how to go about acquiring the knowledge you'll need to buy and use microphones wisely. As always keeping in mind the rules which of course are very very important not to break, except when you do... which is probably quite often.
Take for example the micing of a drum kit. You might think that you should go into the live room and stick a dozen or so close mics on the kit and maybe a room mic and you're done. But think about the flavor that your trying to achieve and add some experience (or the experience of others) to the mix and you may find that you need twice that many mics to get what you want (or half that many!). I'll give away one little tidbit and say that once I was out to record a band with very little time and only eight tracks to work with. I put a D-112 in the kick and an SM-57 overhead. Now I just made a lot of people cringe with that statement but when added in with the bleed from the guitar mics and the singer's mic, you got this great impression that you were right there in the practice space with the band.
So not only should you be filing away all those happy little accidents but also all the ones you read or hear about from other people. Just make sure that you're only using the ones that come from people you trust and who's work you respect. If you buy the hype printed next to each mic in a catalog you're heading down a bad road. But this brings up a great point. How do you know what mic to buy. Again, go to those you trust and you will find out things like for instance, I've heard there's an MXL almost as good as a Neuman U87 (I don't remember which one but I'll see if I can find out). It won't stand up totally of course, but if you can buy a $50 mic that's 80% as good as a $6000 mic you just saved a ton of money you can spend on plugins and such. You've also got a mic you don't have to protect with your life and you can feel a lot better about taking it out on location.
Along with little gems like that there's just a ton of folklore and voo-doo about mics, especially vintage ones. If you're out to buy something old, make sure you get a chance to hear it first. If that's not possible then you should at least request to hear something the seller has done with the mic you intend to buy. Even then you have to be careful and decide just how much the investment is worth to you. If you're pretty well off and a ribbon mic dies in transit you can probably shrug and walk away, or if those 414s you picked up on eBay aren't from the "good" era and so on. The point is, you need to really research your mic purchases well, especially if you can't afford to take a hit.
So to make a long story short, you basically need to get a good body of knowledge together about mics and techniques, know what the rules are, then break them when you need to and get your own sound. If you're sitting in a studio full of expensive condensers but your client is doing a punk record you might be better off reaching for the mics a live engineer would use, instead of getting pristine tracks and trying to dirty them up with plugins.
It's important to think about the room you're in too and decide how you want to hear that. Going back to the example of my quick drum tracking solution. Taking that idea into a piano session I might not even mic the piano, but instead point a condenser at the wall on the other side of a bright room and wind up with a really haunting sound. For a vocalist, it's easy to be lazy and say you'll come up with atmosphere at mixdown. But if you've got a stairwell and an extra mic or two, why not try a take in there with the singer on the ground floor and mics on the landings above. You can always keep the clean track but the reverb you get will be unique.
And while I'm giving away good tricks I won't leave the live guys out. Guitar players are particular about their tone. If they've spent a lot of time on it they want it to come pouring out of your PA the way they hear it at home. I've taken to always double micing a cab if I'm able. Nothing fancy, a 57 and a 609 will do. I position them so that one will give me a fat sound and the other a skinny one. Then instead of wrestling with positioning a single mic and EQing it I can push the fat and skinny channels back and forth against each other till the cancellations and additions between the two sound nice. It may not sound exactly like the cab but you can get pretty close pretty quick. For open backed cabinets you might throw that second mic on the back and flip the phase (polarity actually). Then you've got the option to bring in a lot of resonance or leave it out as the material dictates. One other nice feature of the fat/skinny setup is you can make a solo come to the front of the mix by pushing up the skinny mic while pushing the fat mic down by the same amount. The sound will get clearer and cut through better without actually getting louder which can be critical in small venues.