Your problem is basically a set path tracking problem.
In you case the 'r' is nothing but 'v' and N is the third matrix given in your system equation. You know where you are (x) and where you want to go (v). Now basically HOW you want to go is what will determine your desired pole locations i.e. your system's performance criteria/timing characteristics. This generic plot should help:
Few other generic guidelines (available in literature) that you can keep in mind are:
1) Do not choose the closed loop poles far away from the open loop poles. Otherwise, it will demand high control effort.
2) Do not choose the closed loop poles very negative. Otherwise, the system will be fast reacting (i.e. it will have a small time constant) In frequency domain it leads to a large bandwidth, which in turn leads to amplification of noise.
Hope this helps. Good luck!!