For a realistic looking scene deterministic positions often looks bad. On the other hand too much randomness is also not 'realistic'. What you need for object placement is controlling randomness. Below are three examples. First image displays a grid made irregular by disturbing the positions with an uniform random jitter. Overlapping can be controlled by adding only a small amount of jitter.

Next an uniform random placement. The disadvantage of this strategy is that overlapping can not be controlled.

Last an example with Poisson disk sampling. The term 'disk' means that there is an avoidance radius to control overlapping.