1. Create a new image.
2. Introduce a guide as a center line by dragging the guide out from the ruler. To make a shape that is mirrored horizontally (or across a vertical axis), drag the guide out from the ruler at left.
[NOTE: You will have to have View>Show>Guides turned on to see the guides. To turn on the rulers, choose View>Show Rulers, or Press (Cmd+R)[CTRL-R]. If you drag the guide from the ruler, pressing the (Opt)[ALT] key while dragging will change the orientation of a guide from horizontal to vertical, or vice-versa; technically the guide can be dragged out from either ruler. Alternately the guide can be created by selecting New Guide from the View menu, in which case the rulers need not be visible.]
3. Draw half of the shape that you would like to mirror (see figure 2). Mirrored shapes can be perfect halves drawn all to one side of the mirroring line (like the arrow example in Figure 1) or they can contain some overlap (like the tailpiece example in Figure 1).
The left half of this heart will be mirrored to create the right half so the two sides are perfect mirrors.
4. When the path is complete, select the whole side with the Component Selection tool (A)[A]. If the path is complex (more than just a single closed path) you may want to group paths using the Combine command before the next step. Combining the paths can make complex sets easier to handle.
[NOTE: Be sure all paths are closed before combining, or you may have some unexpected results.]
5. Copy the selected Path.
6. Paste. This will duplicate the path in exactly the same spot you will not see the difference on screen until you move the path. Alternately you can press (Opt+Cmd)[ALT+CTRL] and click and drag the original path to duplicate.
7. Flip the duplicate Horizontally. To do this, use the Transform Path Scale function on the Options bar and change the W [width] setting to -100, or choose Flip Horizontal from the Transform Path menu. If you were duplicating vertically, you would set the H [height] to -100 or choose Flip Vertical.
[NOTE: The input values on the Options bar and Flip Vertical and Flip Horizontal on the menu are only available after selecting one of the basic Transform Path functions.]
8. Use the center line to snap the duplicated part into horizontal alignment. This does not have to be perfectly aligned in the vertical at this point.
This step need only roughly align the two halves vertically. The next step (Step 9) will take care of the vertical alignment.
9. Select the two halves of the shape with the Component Selection tool (black arrow) and use the Vertical Align on Center to align the halves vertically.
[NOTE: Top and bottom alignments work just as well in this case, they would just use different reference points for the result.]
10. Combine the paths into a single shape by clicking Combine on the Options bar.
With the two halves perfectly aligned and combined, the shape is now a perfect whole and ready to be used or stored.
11. Choose Define Custom Shape from the Edit menu. This will open the Shape Name dialogue box, which will contain a preview of the shape and will allow you to change the name. Selecting [OK] will store the shape in the currently open shape set.
12. Choose the Shape tool. This will activate the Options bar for the Shape tool so the shape menus are accessible.
13. Switch to the Custom shape tool. You can do this by clicking the Custom Shape icon on the Options bar or by pressing (Shift-U)[Shift+U] until the Custom Shape is selected.
14. Click on the Custom Shape Picker on the Options bar. This will open the shape picker as a drop palette from the options bar.
15. Choose Save Shapes from the Shape Picker pop-up menu. The pop-up menu can be accessed through the menu arrow at the upper right of the Custom Shape Picker palette. You may want to save the shape set in your Photoshop directory. Saving will save ALL the shapes in the palette currently as a set.