Define the positive convention for the problem. Draw an "x" and a "y" axis and specify the positive directions for the axes as well as for any moments.
Draw a free-body diagram of the system in question accounting for all forces represented. For example, consider a block of weight, "W," supported from above by two taunt cables attached to a ceiling at 90 degrees respectively, and find the static tension in the cables. Draw a square representing the block with two upward arrows going from the top of the box on either side to a horizontal line above, representing the ceiling. Now draw an arrow from the center of the box extending downward, representing the weight of the object. Label the two arrows going up as T1 and T2 and label the arrow going down as W.
Write the equilibrium equations of the system. For example, write "The sum of the forces in the x direction = 0, the sum of the forces in the y direction = 0 and the sum of the moments = 0."
Solve the individual equilibrium equations for the specific system. In the example there are no moments and no x components to the given forces, therefore the only equation to solve is the sum of the forces in the y direction = 0. This yields: T1 + T2 - W = 0 or T1 + T2 = W. Since T1 and T2 must be equal (both are hanging at 90 degrees):
T1 = W/2
T2 = W/2
W/2 + W/2 = W