Three places rub, and only one of them is fixed by lubricating
A floor has three interfaces that can make noise. Board against board at the tongue-and-groove seam, which gives the sharp squeak. Board against its nail or screw, which gives a click as the fastener shifts in an enlarged hole. And subfloor against joist, where a gap lets the whole assembly flex like a small drum under your foot — that is the dull thud with a hint of sink.
Most squeaks are not a defect in the wood and not poor workmanship. They are the normal seasonal cycle: boards shrink in dry air and fine gaps open, then swell in humid air and press against each other. So the fact that yours only happens in winter, or started when the heating came on, is not trivia — it is the diagnosis pointing at friction rather than at a loose fastener.
Powder is a test as much as a cure
Work talcum powder, powdered soapstone or graphite into the seam, cover it with a cloth, and walk on it. The powder is a dry solid lubricant, so it genuinely does stop boards rubbing — and how the silence behaves afterwards tells you what you are dealing with. Quiet and it stays quiet: it was friction, and you are finished. Quiet for a week or two and then back: something is loose, and the powder was only masking the movement until it wore away. No effect at all: it is not friction, so go and look underneath. That is why the powder is worth doing even when you suspect the fastener — it costs nothing and it converts a guess into evidence.
The choice of powder matters for looks rather than performance: talcum and baby powder are white and vanish into pale seams, graphite is black and lubricates identically but will show on a light floor. Two things not to use: liquid wax only belongs on a wax-finished floor, never on a polyurethane or varnish surface; and avoid WD-40 or silicone spray on a finished floor, because a liquid soaks into the seam and leaves a slick, dust-collecting residue that you cannot get back out.
When it is loose, the screw length is the whole risk
Fastening from above is the invisible repair, but only if the screw stays inside the floor. The rule is simple and absolute: screw length is about 6 mm less than the combined thickness of board plus subfloor. 19 mm board on 19 mm subfloor means 38 mm total and a 32 mm screw; on 16 mm subfloor, 29 mm. Drill a pilot about 12 mm shorter than that total, keep the hole at least 12 mm in from the board edge, angle it towards the centre of the board, and — this is the step that decides whether it works — have someone stand on the board while you drive the screw. Then countersink and fill.
From below is more reliable if you can get there: a glued shim between subfloor and joist, or a bead of construction adhesive along the joist top with the floor pressed down while it sets. Do not force a shim — driven in too hard it lifts the subfloor and moves the squeak somewhere new. Siding shingles work better than shop-bought shims because their taper is gentler.