Incorrect threading is the most common cause of uneven stitches. Even if the machine looks threaded correctly, a full re-thread is always worth doing first.

• Raise the presser foot before re-threading - this opens the tension discs so the thread seats properly
• Unthread completely and follow your machine's threading path carefully from the spool all the way to the needle
• Re-thread the bobbin too and check it's inserted correctly

Upper tension that's too tight is the most common cause of puckering — it pulls the top thread taut and drags the fabric up along the seam.

• Start from the default or middle tension setting and test on scrap fabric, adjusting gradually in small increments
• If stitches are puckering, try easing the upper tension back slightly
• Make sure the top and bobbin threads are the same weight — mismatched threads create uneven tension and are a common overlooked cause

A stitch length that's too short for the fabric can cause puckering, particularly on lightweight or delicate fabrics.

• Try lengthening the stitch slightly and testing on scrap fabric
• A good starting point for most fabrics is around 2.5mm - adjust from there based on fabric weight

A dull or incorrect needle drags through the fabric rather than piercing it cleanly, which can cause puckering and uneven stitch formation.

• Replace the needle with a fresh one - when in doubt, always put a new one in
• Make sure you're using the right needle type for your fabric - fine needles for lightweight fabrics, ballpoint for knits, sharps for woven fabrics

Pulling or pushing the fabric while sewing distorts the stitch length and can cause waviness or puckering along the seam.

• Let the feed dogs move the fabric at their own pace - don't push or pull
• Guide the fabric gently with your hands, keeping it flat and supported as it feeds through
• Make sure any excess fabric is resting on the table rather than hanging off the edge, as the weight can pull the fabric through unevenly

Some fabrics are more prone to puckering than others and may need a slightly different approach.

• Lightweight and silky fabrics pucker easily - try a fine needle, lengthen the stitch slightly and use tissue paper or a stabiliser underneath for extra support
• Stretchy fabrics need a ballpoint or stretch needle and a slight zigzag stitch rather than straight stitch, which can break under stretch and cause puckering

Before returning to your project, test on a piece of scrap fabric of the same type. Check both sides - the top and underside should look even, with no loops, puckering or pulling in either direction.