The key to winning the cave of ordeals, is proper preparations. Be warned, this guide does not tell you how to beat it with no skill what so ever, it is here to make it easier.
1. Infinite bombs and arrows
2. All 4 bottles (Guide here) 3 filled with blue potion, one filled with a fairy (The fairy is a backup. If you get hit before managing to drink a potion, the fairy will save you. Also, if you've still got the fairy tears from Jovani, keep that, or if you've beat the cave of ordeals before, and you are doing the harder version, have fairy tears in a bottle instead of a blue potion)
3. 2 clawshots is an absolute must! You can't get all the way to the end without them, as you'll be blocked by a wall.
4. Secret sword techniques (at least the one where you jump, roll and slice)
Extras: Magical armour+Giant wallet (Guide here) The armour can be helpful when fighting the tougher enemies. If you choose to use it, make sure your wallet is the largest one, and fully filled.
Now you've prepared for the cave of ordeals, and you're ready to go.
1. Well, the reason you got infinite bombs and arrows, is, 'cause they are a good weapon. Whenever you can, don't jump down to the enemies, stay at the top, and shoot the enemies with bomb arrows. Most enemies will die from them. Of course, if there are enemies beneath you, you won't be able to shoot them easily, so you will have to jump down, but you can still quickly shoot them from there.
2. The first room, where you have to transform into a wolf, to kill the invisible rats, after you've killed all of the enemies, don't leave the room. In the middle, there is a spot to dig, with three hearts. This is one of the only, if not the only spot where you will find heart refills.
3. Killing zombies: Now these guys are much easier than you'd think. stay a good distance away from them, not to alert them. Now, get out that huge steel ball of yours, get just close enough for it to reach the zombie you've targeted, and throw it. He's dead, if you hit him properly.
4. Killing giant spiders: Well, these guys can also be killed really easily with the ball 'n chain. A little harder though, as they're faster movers, but they shouldn't be a problem.
5. Killing Dark Nuts (Heavily armed soldiers): These are also much easier than you might think. A little harder, of course, when several of them attack at the same time. Well, this is how you easily get there armour off, and damage them after. First, lock onto the Nut. When he's about to swing at you, do a backflip out of the way. Now, instantly, do a jump attack. You might get a few swings at him before he blocks your attacks. Repeat till he has no armour. And watch out when he throws his weapon at you. It's not too smart to be in the way. Now, he's a little more dangerous. If you keep you're lock on him though, at all times, you should be fine. What you do now, is, get close to him. Then do the secret sword technique, where you jump sideways, roll, then slice. This'll knock him off balance, and it gives you a small amount of time to slice him. Just repeat this process, until he dies. With several enemies, try to isolate one, and fight him. THis is hard though, and you will take some damage. If you have got magic armour, now would be the ideal time to use it.
6. (Not necessary, and can be risky) Golden Chu Jelly: Well, in one room, you'll see something glittering in the roof. This is the golden chu. Now, you'll need an empty bottle, so if you don't have any, you'll have to empty one, which is the problem, really, as you might not succeed, and will have wasted a bottle full of blue potion or a fairy. What you do, is, stay at the edge of the ledge at the top. Now, take out your bow, and shoot the glittering part with either an arrow or bomb arrow. make sure you have the empty bottle easily accessible when doing this. Once shot, quickly jump down, take out your bottle, and scoop the puddle on the floor, and woila! Golden chu jelly, which is just like fairy tears! The puddle quickly disappears, which is why you have to be quick. Oh, and once down there, you'll be bombarded by falling Chu's.
What NOT to do:
1. Absolutely NEVER wear the Zora tunic in here! Ice and fire will do crazy damage on you!
I'll keep adding to this, since it's been a while since I played it. If you know any tips, do post them! Hope this helps!