That said, there's a great deal of conflation and confusion about them. Historically, they are legendary creatures of European folklore, thought to bewilder people, steal children, cause mischief, confuse travelers, and enchant any and all things. Functionally, that description really isn't far wrong, as they, while varied, are generally rather good at beguiling others when it suits their needs and wants.
By and large, the Fae answer to one head honcho, and that head honcho is euphemistically known as the Green Man, the Puck, the Night Rider, Blue Cloak, the Corn King, the Holly King, Freyr, Ullr, and a host of other names. There are very specific names he's called when you're interested in approaching the Fae, but that's beyong the scope of what I'm talking about here.
They are nature spirits of a sort, and they are as diverse as we are and plenty numinous, appearing as fair, beautiful creatures ranging from the size of Tinkerbell to the size of us and bigger, or as squat and ugly as Goblins and trolls of ancient myth. The Ljosalfar, Svartalfar, Dokkalfar, Duergar, and all other hosts of elves are too of their banner, and they all have their own tribes and practices. Some are more skilled with word and enchantment while others prefer mining, buried treasure, and smelting. There are very few constants in dealing with them outside of who they ultimately answer to and the fact that they generally don't like humans much.
Even the apparent allergy to metal is something that is entirely dependent upon what sub-race you're speaking of, as the idea of a blacksmith whose afraid of iron is downright stupid. Some of them don't like silver, bronze, or iron, whereas others can't get enough of the stuff and will, if you let them, depart with your nice things in hand - kid you not, in my old apartment 5 pizza pans went missing in the course of two months, never to be found again.
As a general rule, if you want to work with them and you haven't started a relationship, leave offerings of candy, water, and citrus outside and/or build a small house or home for them to visit, then leave. Keep an eye on the fort, so to speak, and see what happens with it. If moss begins to grow on, around, and in it, you'll know you have a visitor. If the offerings were untouched, you either offered the wrong thing and need to ask them to show you what they like or they don't like something about your home, so the same need stands true.
If you see them, there's an old tradition that dictates that you should not be the first to speak, but in reality that depends on what you see and feel, and usually they're trying to tell you something if they show themselves. Listen carefully and really try to feel what they're showing you; it'll make more sense that way. Do not eat or drink anything they offer you, but instead simply bow your head in thanks and let that be that. Never try to look beneath the glamours they show, for that is oft considered to be terribly rude.
If they show up in your home, set ground rules as you should with any spirit. Tell them what they can do and what they can't, and, by and large just try to be a decent host. As a result of my working with them, they play with my cats and watch out for me - there are, periodically, ones that misbehave and get tossed out the front door...these things do happen, as they are tricksters.
On the negative end, being trickster and sprites, if they don't like you, you will know. You will get sick for no reason, probably develop phantom bruises, and will most likely have horrible nightmares for a while. If that happens, stop all work with them, give offerings outside your house, and then clean out your house physically and spiritually; that's a sign that they want nothing to do with you and they will bugger you up if you proceed.
Fae can be downright malicious, so if those symptoms persist, you will probably want to contact me for assistance. When slighted, some of them will continue to screw with you until forced to buzz off.
That's all I can think of to write, for the moment. If you have questions, fire away.
Edited to add:: my mistake, the individual who contacted me is a male, not a female. Sorry about that!