Collect your data. For example, if you wanted to create a graph reflecting the movement of a snail over time, measure the distance the snail covered each minute for five minutes. This will provide you with five data points. For the purpose of clarification, suppose the snail moved two inches in the first minute, one inch in the second minute, two inches in the third minute, three inches in the fourth minute and one inch in the fifth minute. In total, the snail will have moved nine inches in five minutes.
Look at the data you accumulated and determine its range. The variance between the numbers will indicate how large the graph needs to be to fit all of the data. In this example, time varies from one to five minutes and total snail movement varies from one to nine inches.
Draw a horizontal x-axis with a pencil. Use a ruler to ensure the line is straight. This line is representative of the independent variable. In this example, the independent variable is time (in minutes). Underneath the line, label the axis "time (mins)" and demarcate five equally spaced numbers (1-5) to represent the five different minutes.
Draw a vertical y-axis. This line is representative of the dependent variable and should be perpendicular to the left-hand-side of your x-axis. In our example, the dependent variable is movement (in inches). To the left of the line, label the axis "movement (inches)" and demarcate five equally spaced numbers. Because the snail's movement ranged from one to nine inches, assign each value on the y-axis in increasing increments of two (2,4,6,8,10).
Plot your data. Your first data point is (1,2). Find the one-minute demarcation on the x-axis and the the two-inch demarcation on the y-axis. Place your data point where the two numbers meet inside the graph. Draw light, erasable lines if you have trouble envisioning where they will meet. Do the same for the remaining four data points. Do not include the origin (zero minutes and zero inches traveled) as a data point.
Draw a straight diagonal line as near as possible to as many of the five data points as possible. A single straight line will let you determine the slope of the line.
Find slope, or rise over run, by picking two points on the diagonal line. The two selected points will be described as (x1,y1) and (x2,y2). The formula to find slope is the following: (y2-y1)/(x2-x1). For example, if your data points are (3,2) and (5,4), then your equation will look like this: (4-2)/(5-3). This will yield 2/2=1. The slope of your line is one inch per minute.