If you plan to hang multiple small photos in a group, first plan how you’d be grouping them. Create patterns or shapes with them, stagger them up a staircase, mix and match larger and smaller pictures or try and create a collage.
Although multiple photos can create a dramatic effect, they may also look cluttered and very distracting. So use your diligence at all times.
If you want to make a particular picture stand out within a group, give a space of around 3-5 inches on each of its sides.