For the dyer, the fibre world is divided into two types: Protein and Cellulose. Scouring, mordanting and dyeing is different for each type.
Animal (protein) fibres are wools, hairs, and silks
Plant (cellulose) fibres are cottons, linens, hemp, ramie etc..
As mentioned earlier, yarns are the easiest to dye. Woven materials require care to get even coverage. A suitably large dyepot is very important. Tightness of weave is also a consideration. Garments are the trickiest to dye. Watch out for synthetic stitching (it will not take on colour) and areas of wear or perspiration as they will dye unevenly. When using wools, care is required to avoid felting.
See our free lesson on FIBRE TYPES at the Maiwa School of Textiles.