When you’re creating a diagram in Google Drawing or laying out objects in Google Presentations, it will always look better if the alignment, size and spacing of the elements (such as lines and shapes) are uniform.
Google Drawing and Google Presentations offer a couple of tools, namely Snap to grid and Snap to guides, to help you with this. Both tools are available in the View menu of the application by selecting Snap to > followed by either Grid or Guides:
With Snap to grid enabled, when you drag an object with the mouse, it’s movement will not be smooth, but will ‘jump’ in a series of tiny hops, each position corresponding to an intersection on an invisible rectangular grid covering your drawing.
Engage Snap to guides and Drawing will present you with visible guides to help you align objects; these horizontal or vertical lines not only help with alignment, but show similar measurements at various locations in your drawing. When you’re trying to create a box of identical size to another, for instance, the guides will appear to show you when you are close to the correct size:
In this image, the red line has popped into view to confirm horizontal alignment with the nearby elements, while the horizontal scale bars (below the red line) let me size my new element identically with the one alongside. Notice, though, that the height of my new element is incorrect; no problem, after creating my new element I can go back and adjust the height too, until the vertical scale bars tell me I have it right:
As an extra tip, remember that you can work with greater precision if, along with snap to guides or snap to grid, you use the Zoom button on the toolbar to get a closer look at the action.