Identify the surface the force acts on
Draw the free-body diagram
Find the contact surface normal
The normal force is perpendicular to the surface
The normal force points away from the surface
If the surface is horizontal, the normal force is vertical
If the surface is inclined, the normal force is perpendicular to the incline
Use the direction of the surface to determine the force direction
Check whether the object is pushing into or away from the surface
Choose the force direction that prevents penetration of the surface