- Create new square artboard.
- Create a square to fill the artboard.
- Select Square → Object → Path → Split Into Grids…
- Choose grid size, depending on preference. Make sure [ ] Preview box is checked.
- Right Click → Make Guides
- Create squares, circles or any other shapes to the grid.
- Place image wanted on board near shape → Send to back (⌘ + Shift + [ (?))
- Select image and shape and make a clipping mask (⌘ + 7)