Two orbits: When is one in the closure of the other?

Let $G$ be a connected linear algebraic group, let $V$ be a finite dimensional algebraic $G$-module, and let ${\mathcal{O}}_1$, ${\mathcal{O}}_2$ be two $G$-orbits in $V$. We describe a constructive way to find out whether $\mathcal O_1$liesintheclosureof$\mathcal O_2$ or not.