Know what the format changes
A card keeps a measured length tidy and is easy to label, while a skein gives the thread room to hang and can be convenient when you want to pull a controlled working length.
The format does not by itself tell you the thread weight or quality. Read the product details and inspect the actual strand before planning a large project.
Choose for your working method
Cards suit makers who like to cut several consistent lengths and store colours upright. Skeins suit projects where the thread will be used gradually and kept in its original wrap between sessions.
Whichever format you choose, avoid pulling from a loose centre that can create a tangled bundle. Keep the working end visible and return unused thread before it becomes compressed.
Label the colour and remaining length
Write the colour name, brand and project on a small label. This makes a replacement easier to find and prevents a near-match from being mistaken for the original shade.
If you cut a card or skein into project lengths, record what remains. A simple note prevents waste and shows whether you need another pack before the final border.