How do you find the maximum value for shear force in shear force diagrams?

If you yze a simply supported beams supporting normal loads on it. First step is to get the reactions on every support using moment equations. Then identify the degree of the loads acting on the beam. Axial load has zero degress while uniform load has 1st degree so on and so forth. After takin the reactions on the support, draw the shear force diagram. We know that the shear at the supports has the maximum value. Just calculate the area of the shear force diagram from a support to the point of zero shear (usually at the midpoint of the beam) and you will get the maximum shear.