Hold the Ctrl key to snap objects to the grid

Did you know that when you hold the Ctrl key in the Scene view while moving the object its position will snap to the grid?

You can fine-tune your Snap settings by selecting Edit -> Snap Settings from the main menu.

snap settings

 

As you can see, you can not only snap object position, but scale and rotate as well!

 

Your object will snap relatively to its start position! For example, if its X position is 0.5, then it snaps to 1.5, 2.5, etc. To snap your object to the world origin (0, 0, 0), use the Snap All Axes button, or X, Y or Z buttons to snap to only one axis at time.

For more information on how you can easily position your object see the official Unity documentation.