Conversion of units for concentration: mol/l to ppm

The concentration of an aqueous solution of $\ce{Mg(SO4)2}$ is $0.001\, \textrm{mol} \cdot \textrm{dm}^{-3}$.

Find out the concentration of solution and the concentation of $\ce{Mg^{2+}}$ ion in ppm.

How to do this? How to find moles in ppm?

If anyone could clearly describe, it would be great.