Begin with the project, not the yarn

It is very easy to fall in love with a skein before you have decided what it will become. The trouble is that a yarn that sings in a lacy shawl can be a disappointment in a jumper, and the reverse is just as true. Before you part with your money, ask yourself three questions: what is the item, how will it be worn or used, and how often will it be washed? A pair of everyday socks needs a very different yarn from a decorative cushion cover. Answer those questions first and the wall of colour in your local yarn shop becomes far less overwhelming.

Think about the qualities you actually need. Drape matters for anything that hangs. Warmth matters for winter accessories. Durability matters wherever there is friction under a shoe or against a seat. Washability matters enormously for anything a child or a dog will come into contact with. Write these down, and you have a brief your yarn must meet.

Know your fibres

Fibre content tells you more about how a yarn will behave than almost anything else on the label.

• Wool is springy, warm and forgiving. Breeds such as Bluefaced Leicester give softness and shine, while Shetland and Romney are hardier and hold their shape well in colourwork.
• Superwash wool has been treated so it can be machine washed, which suits baby garments and socks. It can grow a little with wear, so swatch carefully.
• Alpaca and mohair bring halo, softness and warmth, but they have little memory, so pure alpaca garments can sag at the shoulders. Blending with wool keeps the drape and adds structure.
• Cotton and linen are cool, crisp and strong. They are excellent for summer tops and home textiles, though cotton is heavy and linen can feel stiff until it is washed a few times.
• Acrylic and nylon are workhorses. Acrylic is inexpensive, colourful and easy to launder; a small percentage of nylon transforms a wool sock yarn into something that will survive years of wear.

Blends are where the magic happens. A wool and silk mix gives sheen and drape; wool with a little cashmere feels luxurious next to the skin; cotton and linen together make a lovely, honest summer fabric.

Weight, ply and what the label really means

Terms such as 4-ply, double knitting and aran describe the thickness of the yarn, and therefore the tension (gauge) you will work at. Lace, 4-ply, DK, aran and chunky form a rough ladder from finest to thickest. Ply is the traditional British way of describing this, but it is not a reliable measure on its own: two yarns both called 4-ply may knit up at noticeably different tensions because of fibre, spinning method and how airy the yarn is.

Always trust the tension square and the metreage printed on the band. Metres per 100g tells you how far a ball will stretch, and it varies wildly between yarns of the same weight. A dense, tightly spun yarn may contain far fewer metres than a lofty one of the same thickness. If you substitute, compare metres rather than ball counts, and knit a tension square before you begin.

Matching yarn to the item

Garments live or die by drape and memory. Jumpers and cardigans work beautifully in wool, wool blends and cotton blends with enough elasticity to return to shape. Choose a yarn with good stitch definition for cables and textured patterns, and something smoother for intricate lace.

Socks need resilience. Look for a tightly spun yarn with a little nylon, or a sturdy wool such as Bluefaced Leicester. Lofty, soft yarns feel lovely but wear through quickly at the heel.

Hats, gloves and scarves are the place to play. A silk and mohair laceweight makes an ethereal shawl; a chunky merino makes a hat you can finish in an evening. Just be honest about itchiness if the item sits against the forehead or neck.

Home textiles need practicality. Cushions, blankets and washcloths are washed often, so cotton, linen and easy-care blends are sensible. A wool blanket is wonderfully warm but requires gentle hand washing, which is worth knowing before you cast on a king-size project.

Swatch, buy enough, and keep a note

Swatching is not a chore, it is a conversation with your yarn. Knit a square at least 15cm across, wash and block it exactly as you intend to treat the finished item, then measure. Fibres behave differently after their first bath: cotton shrinks and tightens, alpaca blooms and relaxes, superwash wool can stretch.

Buy enough yarn in one go and check the dye lot on every ball, as shades can shift subtly between batches. If you are working with hand-dyed skeins, alternate them every couple of rows to blend any variation. Finally, keep a small note of the yarn, the needle size and your tension with the finished piece. It will save you guesswork the next time you stand in front of that wall of colour, wondering where to begin.