An incorrectly inserted bobbin can disrupt the sewing machine's timing, leading to the needle striking the bobbin case
For most machines, the flat side should face towards the back of the machine. And did you tighten the needle clamp screw firmly to secure the needle in place.
Lint can disrupt everythig and cause needle breakage.
Select a needle appropriate for the fabric and thread you're using.. Some machines take round needles and some fla backed
Lightweight Fabrics (e.g., voile, chiffon): Use a size 70/10 needle. Heavyweight Fabrics (e.g., denim, canvas): Opt for a size 90/14 or 100/16 needle. Knit Fabrics: Use a ballpoint needle (sizes vary based on fabric weight) to prevent snagging of the fabric
When threading a sewing machine, the presser foot should be in the 'up' position.