I am doing DFT calculations with pw.x executable in Quantum Espresso. For this we have to choose right K-points grid in order to perform error-less calculation. But I have no idea about how can I choose optimal values of K-points? How to converge it?
Do I have to perform same calculation with different values of K-points (by randomly guessing it).  

What will be the effect on band structure if I take very high values of K-points or low value of K-points?

Please, clarify my doubts.
Thanking you!