How do I calculate the force to pull a load up an incline if the following are known?

Weight of load
Coefficient of Friction
Angle of Incline

To pull the load up the incline you need to pull hard enough to overcome the resisiting forces of gravity and friction. The resistance due to gravity is equal to the object's weight times the sine of the angle of incline. The resistance due to friction is equal to the object's weight times the cosine of the angle of incline times the coefficient of friction (the reason why cosine is used is because friction is calculated using the normal force of the object's weight against the incline). Add these two resisting forces together and you have the amount of force it takes to keep an object moving at steady velocity up the incline. Pull harder than that and the object will accelerate up the incline. Pull less hard and the object will either (a) not move at all, or (b) slide backwards.