Measure with the project in mind
Use the cloth width, stitch density and your comfortable arm span as a guide. A working length should reach the next stopping point without creating a long loop that catches on the fabric.
When learning, cut shorter lengths and accept more joins. It is usually quicker to secure a new length than to undo a knot deep inside a stitched area.
Keep both ends controlled
Hold the skein or card in one hand and the cut section in the other before separating it fully. Place the loose length straight on the table rather than letting it fall into your lap.
Use sharp fabric scissors or thread snips for a clean end. A crushed cut can fray while you thread the needle and make the first few stitches harder to place.
Make a repeatable station
A ruler, paper strip or marked piece of card can give you a consistent measure. Keep it beside the project so each session begins with the same simple routine.
Return unused thread to its labelled storage rather than mixing short pieces together. Separate colours and weights remain easier to identify and less likely to knot.