Let $G$ be a finitely generated group, ad let $(V,\rho)$ and $(W,\phi)$ be two finite dimensional linear representations of $G$ over $\mathbb{R}$. Given a linear map $f:V\to W$ it's immediate to check whether $f$ is equivariant or not, but I find it hard to find an equivariant map if I'm not given one.
Is there any results that classify or characterize all the equivariant linear maps between the two?
Just take an arbitrary linear map and average it over $G$.