I take clothes that would be otherwise thrown away, things the thrift store was getting rid of or donations from my professional organizing clients, and #1 fix / mend / replace buttons if needed and then add on some kind of words or combine other upcycled textiles to make the clothes more interesting.
If I modify something like cutting off the bottom of a sweater to make it a crop, I try and use the fabric on the garment itself by moving it to the shoulder to make ruffles and change the silhouette without creating textiles waste.