Don't use a humidifer. That is a big no no. Use 16 oz. clear plastic cups as humidity domes. That way you can avoid the mold on the walls which should be cleaned off asap with a bleach solution.
Some varieties are easier to clone than others. There are Sativas that will sprout roots so easy, you can (almost) stick them in the ground and forget em. But then there are some early Indicas that you can baby and they will just sit there and starve to death. So there are a few things you have got to look at.
Help the roots grow. Figure out where the roots will grow on your cutting before you actually cut it. Keep this portion of the stem dark for a week or two by wrapping some tape around it. This is called "etiolation" and will encourage rooting. Make the cutting with a sharp anvil pruner or very sharp scissors, and sterilize them after each cut. A dull pruner will crush the stem and it will be harder for the roots to form. A razor blade will make an even cleaner cut, which will also help rooting, but don't blame me if you cut yourself. Try to make the cut at angle to increase the surface area it has to absorb water.
The plant needs air to help the roots form, but don't let any get in the stem. This will cut off the capillary action and make the poor cutting work harder. Immediately dunk the cut end in water or rooting solution to prevent this from happening. You could even take it over to the sink and make a second cut under running water if you're really worried about it. Leave it in the rooting solution for a day or so. If you just leave it in the water, you might get lucky and sprout some roots, but they really need some oxygen. You can actively provide O2 by aeration or passively aerate by using an airy medium.
Another thing that makes the cutting work harder is breathing itself. Use a plastic dome or humidity tent to limit transpiration and keep the medium from drying out, and. Half of a 16 oz plastic drink bottle fits right on top of a 3 inch clay pot. Another way to limit transpiration is to cut about half off of each leaflet. You will still have the same number of leaves on the stem, but the surface area has decreased. This also helps control fungus by preventing the leaves from contacting the dome or the medium.
The proper lighting is also important. Direct sunlight will heat the air in the dome too much, but they're not going to root in the dark either. Fluorescents are ideal for this. An HID is OK if it’s not too close, or you could even give them a bit of indirect sun from a window if you can keep them warm.
You’ve kept an eye on the pH and the nutes, and you see it’s starting to grow again, so its safe to assume that it has roots and you can remove the humidity dome. Occasionally a cutting may wilt a little at first, but give it a mist and it should perk up. If none of these tips help, either consider tissue culture or finding a different mother.
