When designing with rags, I usually make a plan, a blue print, to follow as I go, based on the amounts of weft I have. Using recycled materials means I sometimes have really limited resources as far as color choice goes, but I still want to make things that look good, right!!
When weaving I often use two thirds of recycled textiles and one third of industrially produced weft; of course preferrably from recycled cotton too. The reason for this is mainly esthetic; if I have some recycled textiles that are really bright and colorful, the result becomes too busy on the floor if I use only those.
Using evenly toned weft next to colorful rags makes the shades more interesting and visually appealing in your home interior. Of course, sometimes I have some really cool shade of recycled fabric but I only have very little of it. Using complementing shades in single-toned weft stretches the amount I have.
Rags transformed from textiles (lower right corner) to balls of rags and lastly woven into a rug (underneath).