Grouping rests 

Just like notes, we have to follow certain rules while adding rests in a musical notation.
1.We use the semibreve rest usually for an entire bar of silence, irrespective of the time signature. We simply put it in the middle of the empty bar   
2.We use the minim rest only where it would be possible to beam 4 quavers together in a 4-4 time signature bar. The hidden or imaginary barrier rule still applies in the case of rests.
3.We need to use 2 crotchet rests where we need two beats of silence in a 3-4 time signature, we should not use a minim rest.