How do you apply bathroom grout correctly without it constantly being dragged out?

"Grout is the stuff you apply between tiles to seal them in place. Grout tiles once the adhesive has dried fully (24 to 36 hours later). The best grout is waterproof and mould-resistant; some come ready-mixed. Use a grout float - a rubber-faced tool with foam backing - for large areas. Spread the grout across the tiles at right angles to the joins. Use a damp sponge to remove excess. Once the grout is dry, polish the surface with a dry cotton rag."

I was taught by a contractor to apply and clean the grout diagonally.