Is it better to wet the toothpaste, or to squeeze it onto a dry brush?

It is better to squeeze a pea-sized amount of toothpaste onto a dry brush. Wetting it makes foam appear sooner, which feels as though you have brushed for a long time, but it dilutes the abrasives and active ingredients, so the actual cleaning effect drops. Plenty of foam does not mean better cleaning - what matters is how long the bristles stay in contact with the tooth surface. Brush for 2 to 3 minutes at a time, following a set order so no tooth is missed.