its easiest if you put it in y = mx + b form, where b is the number you plot on the y axis and m is your slope.
rearranging...
x + 3y = -5 3y = -x - 5 y = -1/3 x - 5/3
so your b value is -5/3, which is where you'll plot a point on the y axis. the slope is -1/3
since slope is rise over run, [and this case its negative] you'll go down 1 and to the right three.
edit: then draw a point there, connect the points, and you'll have a line =]