1. The surfaces in contact are rougher: The more irregularities and bumps there are on the surfaces, the more they will interlock and resist movement.

2. The surfaces are pressed together with a greater force (normal force): The harder you push two surfaces together, the greater the force of friction between them.

3. The surfaces are made of materials with a higher coefficient of friction: The coefficient of friction is a property of the materials in contact that determines the amount of friction generated. For example, rubber on asphalt has a higher coefficient of friction than ice on ice.

In summary:

* Rougher surfaces = More friction

* Greater normal force = More friction

* Higher coefficient of friction = More friction

Let me know if you want to dive into specific examples!