What would be most helpful to find the normal melting point and normal boiling point on a phase diagram?

On a phase diagram, pressure (the $y$ axis) is plotted against temperature (the $x$ axis). The pressure scale has units of $\text{atmospheres}$ typically, and the temperature scale naturally has units of $\text{degrees Kelvin}$. Under conditions of low pressure and high temperature, the substance exists as a gas, and at low temperature and high pressure, the substance exists as a solid.
Now the normal melting and the normal boiling points, by definition are the temperatures at which the solid changes to liquid, and the liquid changes to gas at $\text{ONE ATMOSPHERE}$. So simply draw a horizontal line on the $y$ axis, and note the $x$ intercepts of the transitions to give these properties.