A speck under a fresh sheet is recoverable. Lift the nearest corner, take the particle off with a dust sticker, lay it back down. The adhesive tolerates two or three lifts before it stops being worth it, so spend them carefully.
Which bubbles clear on their own
Small bubbles around the perimeter, smaller than a grain of rice, with no visible speck at the centre: those are adhesive still wetting out against the panel. Leave them. They close within about a day and pressing on them achieves nothing except moving them somewhere else.
A bubble with a hard point at its centre will never clear. There is something solid in there holding the gap open, and no amount of time or pressure changes that. Look at it against a light at a shallow angle — a dust bubble has a dot, an air bubble does not.
The lift
Fold a strip of tape back on itself to make a tab and stick it to the corner nearest the speck. Pull slowly and roughly along the plane of the panel, not up and away — you want the adhesive to peel rather than snap, and you only want to lift as far as the speck.
Hold the raised part by its edges. The adhesive survives being lifted; it does not survive a fingerprint, and a thumbprint on the underside is worse than the dust you went in for.
Take the particle off the sheet, not off the screen. Touch a dust sticker or a strip of tape to the adhesive side where you can see the speck, then to the panel underneath it.
When to start over
After three lifts the adhesive has picked up enough from the air that it will not wet out properly again, and you will be trading one speck for a general haze. That is the moment to take the sheet off and open the next one — which is the argument for buying a pack rather than a single.
Also start over if you have touched the adhesive face, if the sheet has been face-down on any surface, or if you can see a smear rather than a speck.
Not getting the speck in the first place
Run a hot shower for two minutes and leave the room to settle. Steam pulls airborne dust down and gives you about ten minutes of the cleanest air in the house. Clean in three passes — alcohol wipe, microfibre, tape for the dust — and check at a shallow angle before the backing comes off.
Questions people ask
How do I get dust out from under tempered glass?
Fold a strip of tape into a tab, stick it to the corner nearest the speck and lift the sheet slowly along the plane of the panel, only as far as the speck. Touch a dust sticker or clear tape to the adhesive side where the speck is, then lay the sheet back down. Hold it by its edges throughout.
How can I tell a dust bubble from an air bubble?
Look at it against a light at a shallow angle. A dust bubble has a hard dot at its centre and will never clear on its own. A small air bubble near the edge with nothing in it is adhesive still settling, and it closes within about a day.
How many times can I lift a screen protector?
Two or three. After about three lifts the adhesive has picked up enough from the air that it will not bond flat again, and you trade one speck for a general haze — that is the point to fit a fresh sheet.
When should I start again with a new sheet?
After three lifts, if you have touched the adhesive face, if the sheet has been face-down on any surface, or if you can see a smear rather than a speck.