Mathematically state the form of your function and understand the appearance of this function. Before plotting an economic function, you need to know what a mathematician would call this function as well as what it looks like. Perhaps it is linear, quadratic or exponential. Be clear on this before you attempt to plot. For example, if you want to plot the supply and demand curves Qs = 10 + 5P and Qd = 60 - 3P you will be plotting mathematically linear functions. Thus, you will be plotting straight lines.
Define the x and y axes. The x axis is horizontal and represents the independent variable's value -- this is for the variable that you are less interested in. The y axis is vertical and represents the dependent variable's values -- this axis is for the variable that is of more interest. For supply and demand, economists are usually interested in how price changes as quantity changes. Hence, the x axis is quantity and the y axis is price.
Find the important points for your functions. So-called important points will be those that you can interpret as being interesting. These points are often function maximums or minimums. In the example with supply and demand curves Qd = 60 - 3P and Qs = 10 + 5P you will have special points for each curve. For the demand curve, the minimum is when P = 20 and the maximum is when P = 0. This gives the points (20, 0) and (0, 60). For the supply curve, the minimum is when P = 0 and there is no maximum; however, we can choose a point that gives the same maximum as the demand curve by letting P = 10. This gives the points (0, 10) and (10, 60).
Plot the special points of your functions. Since the axes have already been defined, you can easily plot the special points that you found in the previous step. Do this for each function. In the supply-demand example, you will plot four points -- two for each function.
Connect the special points of each function in the mathematically appropriate way. Keeping in mind what type of function you are handling and for each function connect the points you have plotted. For example, because the supply and demand curves given are linear functions, connect them with straight lines.