Print a text on paper. Use a large angular font and tape the paper on the wall. Use a spirit level meter to check if it it straight.
Hammer the nails into the corners of the letters. Remove the paper after that.
Take the wool (or other rope). Start by making a knot around the nail of the lower left part of the first letter. Then, go to the next nail and wrap the wool once around the nail before going further.
Go further with the same strand of wool. Don't make knots, just wrap around.
Make a knot at the last nail and cut the the rest of the rope.
Try to use only one strand of wool to make a word. Some letters are hard, an A or O for example. Use extra parts of rope then to complete. I used two extra small strands to make an A.
A different color will make it even more attractive.
And this is the final result :)