Understand the movement
A palm thimble gives a firm surface against which the needle can be rocked or advanced through several stitches. This can feel natural on flat cloth and repeated rows.
A fingertip thimble protects the end of one finger and suits makers who push the needle in a more direct motion. Neither shape guarantees better results without practice.
Match the layers and needle
Thicker denim, patches and firm cloth may benefit from stronger support. Fine cloth may need a lighter touch so the thimble does not encourage excessive pressure.
Try the thimble with the actual needle and thread. The correct fit lets you guide the shaft without losing contact or squeezing the hand tightly.
Choose comfort over tradition
Wear the thimble for a short swatch and note pressure points, slipping and hand fatigue. A tool that protects one place but creates strain elsewhere needs adjusting.
It is reasonable to use different thimbles for different projects. Keep the one that helps you maintain smooth tension and a safe needle path.