Now that you have created a guide layer, you can draw out your guidelines.
Click once on the guide layer. The Pencil icon that appears next to the name indicates that the layer is active and ready for editing.
Choose the Line tool from the drawing toolbar.
Select the Line Color button and, from the pop-up color picker, choose white (see figure 02:07).
Draw a straight line down the stage. Hold the Shift key down as you draw to ensure a straight line. The line size doesn't matter; you'll adjust that next.
While the line is selected, choose Window > Inspectors > Object to open the Object Inspector. Alternatively, you can use the keyboard shortcut Ctrl-Alt-I / Cmd-Option-I.
Enter 10 in the x (horizontal) field and in the y (vertical) field. This moves the line 10 pixels from the left, creating a margin.
Enter 400 in the h (height) field to match the dimensions of the stage (see figure 02:08).
Notice that the line, when deselected, is the color of your guide layer outline boxin this case, blue. You can set that color by double-clicking on the Guide Layer icon and selecting the Color tab.
Now the idea is to repeat this process in order to define a 10-pixel margin around the stage as well as a center point.
Select the line and choose Edit > Copy or use the keyboard shortcut Ctrl-C / Cmd-C.
Paste the line by selecting Edit > Paste (Ctrl-V / Cmd-V).
The line is pasted in the center of the stagewhich is exactly where you need a line for your center axis.
Duplicate the selected center line by choosing Edit > Duplicate or by pressing the keyboard shortcut Ctrl-D / Cmd-D.
In the still-open Object Inspector, move the newly created line to the right margin by changing the x value to 540 10 pixels fewer than the stage's width, (550)and the y value to 0.