To align props and characters to boundaries of other objects, use The Snapping Feature. If you need a tighter grid overlay to perfectly align your assets where needed, follow these steps.
Step 1. Save and download the Gridlines PNG file attached below
Step 2. Import it as a Prop > Add to scene
Step 3. Scale it out as much as needed to cover the stage
You can now add your assets to your scene. Delete the gridline prop when finished.