As always, there are lots of ways to do this and this is the way I prefer! There are some steps so hang on with me! and Ask any questions in the comments section!
So, I had a customer ask about how to make this nice little stroke inside a shape, like so:
1. Either leave your shape as a vector shape (no texture added) or duplicate the shape, and mask the duplicate so that it's just one color. This is so the next step will work...
2. Next, grab the Magic wand tool from the side toolbar.
Select the shape. The whole edge should now be selected with dancing ants.
3. Now go to Menus along the top, find Select----> Modify---->Contract
4. Make a new layer above your shape.
Now, go to the Paths Menu above the layers palette.
Oh man! sorry, I am pointing at Styles in this screen caption, oops! but see the tab below it? Paths. You have Layers, Channels, then PATHS. That's the tab you want. Sorry about the goof!
5. In this menu, find the button at the bottom with the circle with arrows on both sides, should say "Make work path from selection". Click it!
6. Now the selection has become a solid line instead of the marching ants. We're ready to make the stroke. Go to your brush palette and find a round brush. Hover it over your shape to get a feel for the size you're going to want. I used 12px.
7. I also like to set one option in the Brushes Palette. My palette is in a side bar next to my layers, on the left side. Go under "Shape Dynamics" and under "Angle Jitter" select "Direction" from the drop down box. This helps our stroke hug those curves and bends!
8. Now, go back to the Paths Menu and find the open circle button at the bottom that says "Stroke Path with Brush".
9. Your stroke will now appear in whatever color your foreground is. You can always change it. Also, if you don't like the thickness, hit undo, and choose a different brush size and stroke the path again! Just keep playing with it until it's the thickness you like!
10. One last step besides adding texture or clipping whatever paper you want to the stroke: Delete the work path. I promise this doesn't delete your stroke, just deletes that line showing where we selected. Hit the little trash can button. Now you can go back to the Layers Palette and you will have that stroke on a layer on it's own.
Voila!! You made it! I know that was a lot of steps but I have found this method makes the best-fitting stroke for a shape! Let me know if you found it helpful or if there are any steps you want me to explain better!