Measure the two bases of the trapezoid. Place the zero marking on your ruler flush with one end of a base. Align the ruler with the line that composes the base and read the marking at the other end of the base. Stand directly above the ruler as you read the marking in order to get the most accurate reading possible. Do this for the other base as well. The bases will be the two sides of the trapezoid running in the same direction, since they are parallel.
Measure each of the legs using the same procedure you used to measure the bases. The legs will be the sides of the trapezoid that run at various angles to the bases.
Measure each of the four angles of the trapezoid with a protractor. Place the center point of the protractor on the point at which two of the sides intersect. Align the zero marking on either side with one of the sides of the trapezoid. Read the marking intersected by the other side of the trapezoid. If the angle is less than 90 degrees, read the inner measurement marking. If the angle is greater than 90 degrees, read the outer measurement marking.