I am making a ton of ribbon roses right now for something semi-arbitrary after like 11 years of not making any, so here's a note to me in case I ever forget how to make them.
Necessities:
Ribbon (For beginners, use a stiff ribbon that can take a fold. Soft ribbon looks nice, and can be used, but it slides around a lot and it's not great when you're learning the steps. Any size, in theory, but I learned 1.5 inch width and that needs to be 3 feet long. There's supposed to be a specific ratio between the width and length, but I unfortunately eyeball when it comes to other sizes because I do not remember the math. The longer the ribbon, the more layers in the rose, but the 3ft for 1.5in looks good.)
Stapler (Technically anything that can hold the ends of the ribbon in place. I'm sure there's other ways, but I was taught to make these in a high school class by a guy who passed around some plier staplers because they were great for other ribbon projects.)
Mechanical pencil (Any thin rod that won't poke through the ribbon will help. I don't use the pencil, I just use the narrow tip, so something like a chopstick or the like will also work.)
Start at one end of the ribbon and fold it at a right angle about 3 inches down. Either direction, doesn't matter, but you'll want to basically rotate in the direction you start in.
Fold another right angle, in the direction of the start point. Leave some space between the starting point and this line of ribbon, they shouldn't be flush. (Not a lot of space, roughly a few millimeters.) We don't want to zigzag, we're gonna be overlapping things soon.
Another right angle, passing over the initial starting bit of ribbon. Again, don't have the ribbon sides flush with the first fold. We should have a large square with the folds, with a small empty square in the center. It shouldn't completely cover the start, there should still be a section sticking out underneath. (We're going to want that extra bit later.)
The fourth fold should continue the square, and from here you follow the previous folds, making layers of squares. Try to leave the space in the center, though it may get difficult to maintain as more layers are added.
When you run out of ribbon, take the other end of the ribbon (the one currently on top, not buried beneath the squares) and carefully thread it through the empty space in the center of the squares. I tend to make sure I have a throughway with my mechanical pencil, take it out, and then try to use it to push a corner of the ribbon all the way through so I can tug the rest of it through on the other side. Only about an inch needs to be pulled through.
Carefully grip the rose, and start twisting the end of the ribbon that was pulled through the center. Try not to pull (it will mess up the center of the rose), and twist in the same direction that the ribbon was folded in. (If folded clockwise, twist clockwise; if counter, then counter.) As you twist, the layers should start tightening and looking more like the rose we're trying to make. Twist until all the layers have pulled up around the center (outer layers can be looser, just don't let the other end of the ribbon fall and start undoing layers).
Line up both ribbon ends together (the starting end and the twisted end) and staple them together. I try to staple along the twisted end, specifically, to help it not untwist. I tend to make 2 or 3 staples to make the end look nicer, but it just needs enough to keep everything from unraveling. (Though I don't do anything special to keep the ends from fraying like I know some people do. I just make these on impulse, not for anything professional, so I tend to just fold the bottom up to where it's under the rose and do a final staple directly underneath where it won't be seen.)
If the rose still looks tight (which it probably will), you can twist the body of the rose the opposite way to make it loosen up. It it looks too lose, twist it in the direction it was folded. It's decently adjustable.
And at this point, it's finished, and if you want to attach it to something, you can. This type of ribbon rose was taught in a class where we used floral tape to put on the ends of pens as fun decoration. It can be attached to all sorts of things in that way alone, but there was also an option to tape them to individual wires to make bouquets or to stick/hang around for general decor. I made some small ones using 1/4in ribbon at my grandmother's request because she wanted to sew them onto a dress. (Which is where I eyeballed the ratio of what length of ribbon would work. It came out pretty well, and she still has the dress, it was for a special occasion.)
I've also had success in making two tone roses, which was basically me putting two ribbons on top of each other and offsetting them a bit, but keep in mind it functionally makes the ribbon you're folding thicker and therefore you need to make it longer to get the same fullness in the rose. Since you fold it over and over, you can probably also just stack them on top of each other, and the two colors will flip flop along the rose petals. If you use two of the same color and put a second color in between but just barely showing, it becomes striped petals. It's super versatile to play around with when you get the hand of it.