Protect the fibre
Use a dry drawer, box or closed project pouch away from direct sunlight, moisture and sharp points. Dust and repeated rubbing can make a soft thread harder to handle.
Avoid tight rubber bands or clips that crush one spot for a long time. A loose paper wrap, card or the original manufacturer tie is usually kinder to the thread.
Keep colour information attached
Store the brand, colour name or number and length with every partial skein. Similar neutrals and blues are difficult to identify later from memory alone.
Group by project before grouping by colour. A dedicated pouch for a repair keeps the correct needle, cloth sample and remaining thread together when you return to it.
Check stored thread before use
Look for dust, fading, moisture damage and new kinks. Test a short section if the thread has been stored for a long time or in a room with changing humidity.
If the strand has become compressed, loosen it gently and cut a fresh working length. Do not pull hard from the centre of a tangled bundle.