Limit cases in sobolev embedding

Question

I am trying to find coumterexamples for the critic cases in sobolev embedding theorem for all $\mathbb{R}^N$. For instance, a function $u\in W^{1,p}(\mathbb{R}^N)$ s.t. $u\notin L^q(\mathbb{R}^N)$ for $q>Np/(N-p)$. This is the case of $1<p<N$. Can anyone give me an idea or hint of how to do it for the other two cases $p=N$ and $p>N$. I am really stucked.

Thanks in advance.