The yucca plant is one awesome plant that can be used to make cordage. The process is easy as you will be using the yucca leaves and its fibers. No dealing with materials with knobs or thicknesses that vary greatly from one end to the other. Easy, here is how.
First you will need to cut or break off a few of the leaves from the yucca plant, then cut of the sharp tip. Long leaves provide the longest fibers, but some of the shorter leaves can be used as well without issue.
Once you have collected a few yucca leaves from a live yucca plant you need to scrape the dark green off of the leaf by laying it on a flat surface and using some pressure and a spoon, rock or other object to scrape off the outer leaf covering. You don't want to scrape to hard or with too sharp of an object which could damage the fibers. The green comes off easily and a lot of work means you are probably doing something wrong. Like I said, easy. Do the scrapping on both sides. Shouldn't take more than a minute per leaf.
The scraping also begins the process of separating the leaf fibers. If the leaf has begun to dry, soaking it for a while can make the yucca easier to work with. Dry yucca is harder to twist, but if you soak it for a long time the cordage will tend to be looser. So don't soak it for a couple of hours or more!
Next simply use your fingers to separate the fibers. The fibers get thinner to the end but just lay some one way and some the other as you separate from the leaf and lay the fibers down like how you buy spaghetti.
Gather up a few of the yucca fibers that are half the thickness you want for making string. Two or three should be enough for string depending on how thick you want your string and how finely you divided the fibers. Rope can be made by simply using more yucca fibers in each string. Most of your needs will be served by string.
Now before you start the string making process you must do something that at first is a bit counter intuitive. Don't line up the ends. Ideally not lining up the ends will ensure that all ends do not reach the need for replacement at the exact same time. So before starting you yucca fibers will be staggered. Hope that makes sense.
Now pick a spot near the center and fold the fibers in half. This will give you the entire thickness of the string. That is why I said start with half a sting thickness you want because you will double it on itself to make it twice as thick.
Pinch and hold the string right were you have it double over. At this point you should have basically two groups of fibers from each of the two ends of your starting fibers. The ends will be loose and of uneven lengths.
From now on I will refer to the two ends as if they are totally separate strings that we are twisting together. Your left hand is the pinching hand and is holding the string near the doubling over area. With your right hand grab the top fibers / string and grab it with your right hand about a half and inch from your left hand's fingers and twist the top string away from you. About three twisting motions should be enough to wind the string together tightly .
Then pull the bottom string towards and upwards. You are twisting the two strings together swapping positions of the strings so that what was the top is now the bottom and what was the bottom is now the top. Keep repeating this process.
After a few turns you will possibly feel the two strings getting thinner. This happens because one by one you will reach the end of the individual yucca fibers. So, they must be replaced.
I believe it is best to take a yucca fiber and add it to the left pinching hand at its center allowing half of the new fiber to be incorporated into each of the two strings (upper and lower).
So quite frequently you will be adding new yucca fibers to your string to make your cordage. Just keep on adding yucca fibers to make the cordage as long as you want. To end your string just tie a square not in the end to keep it from untwisting itself.