Measure the friction force between the two surfaces
Measure the normal force pressing the surfaces together
Use the formula μ = Ff / N
Divide the friction force by the normal force
For static friction, use the maximum force just before motion starts
For kinetic friction, use the force needed to keep the object moving at constant speed
Use consistent units for both forces
If using an inclined plane, find the angle where the object just begins to slide
Use μ = tan(θ) for the angle of impending motion on an incline