Fresh-pressed, sweet cider. check that there's no preservatives, because that stuff works, and you're trying to rot your cider, not keep it fresh.
The easy way:
a rubberband (to hold the cheeseloth over the mouth of the jug)
The fancy way: (you can get it all from a home-brew place)
A brewing bucket/carboy
a gravity-measuring device (for knowing how strong yer drink is!)
siphon (if you're going really fancy)
bottles and associated accouterments
The easy way (taken from the one, the only, Sandor Ellix Katz who brought you the definitive Wild Fermentation*:
Put your cider in a jug/jar/whatever. Cover the mouth of the jug with cheesecloth so nothing but wild yeasties get in, and wait. taste from day to day. Sandor says that in one week you should have a good, alcoholic, bubbly hard cider. But be careful - if you wait too long you'll have no choice but to let it become vinegar because it'll be well on its way. When it's done to your liking (tastes alcoholic but not sour) put a lid on it and put it in the fridge! Share with friends, who will love you a little more after a few cup fulls.
The fancy way (supposedly this comes out better and harder - also, it's more easy to manipulate and keep clean. this is the method I'm using):
A note up-front - know your ingredients. If your campden tablets say one thing, and I'm saying something else, use the information on your tablets. If you're not sure, ask someone who knows. There's bound to be a home brewing store somewhere around you. Ask around and you'll find it. If not, ask a farm stand that has sweet cider. they might home brew their own hard cider and be able to give you pointers.
Measure your gravity. (do this be reading the instructions on your gravity-measuring device (I'm sure it has a name, but I've forgotten it)). Record it in your homebrew journal, or wherever you keep numbers you'll need to know in two weeks. basically, you're figuring out the sugar-to-water ratio in your cider which will tell you just how alcoholic your brew can get, since yeast converts sugar to alcohol. The more sugar, the more alcohol. Or, if you like bitch drinks, the sweeter and less alcoholic.
Prepare a yeast starter (like you would for bread, but with sugar and no flour). 1 cup warm water, 2 tablespoons sugar, the yeast, and my recipe (from the homebrew store in town) called for citric acid. I had no citric acid, so I used a squeeze of lemon, and it seems to be working fine. Also, I'm skeptical of how much this bit of acid is actually necessary (but don't exclude it just because of my speculations - let me know if you've heard something on this topic). Cover and set aside for 24 hours.
Empty your cider into your brew bucket/carboy. Wherever you're starting your brewing (probably the bucket). Now throw in some yeast nutrient (about 1 teaspoon per gallon of cider) and Campden tablets (crushed). 3 pills for 5 gallons were my instructions. Also, if you're going to add more sugar, now would be the time to do it. Cover and set aside for 24 hours.
...wait 24 hours (remember: a watched pot never boils)...
You're through waiting! Now stir the hell out of your cider until it's frothy on top to get any sulfites that might be hanging around out of it. once it's really stirred up, throw in your yeast nutrient (common-sense yeast etiquette: your liquid should be room-temp - yeast doesn't like the cold), cover your bucket, put on the airlock (don't forget to fill it with water like I did!), and put it somewhere safe and with steady temperatures.
If you don't have steady temperatures (like me), put your brew up on a stool (off the cold floor) and wrap it in a blanket. This will at least moderate the swings in temperatures.
...wait 2 weeks, or until the bubbles stop in your airlock...
Now either rack into bottles and fridge it, or siphon into a carboy for clarification and continuing fermentation. I haven't gotten to this part yet, so I can't tell you how to do it. I'll update you when I get there.
Painless, no? And you thought home brewing was hard!
*I truly believe that this book will become a must-have classic. Get your limited first editions now! In neon green and hot pink, this ugly little book will be a sure-fire crowd pleaser in twenty or thirty years when they're in multiple editions and have chosen a more attractive cover. the coveted, ugly first edition will be a marvel to behold. That and it's a damn good book - what's stopping you?