Many Photoshop users are unaware that an object can be stroked and filled multiple times. The key is the fact that strokes and fills can be applied without using any layer styles. Here's how to do it.

1. Draw a circle roughly this size.
   
2. Choose 'edit > stroke' from the top menu, then enter the following settings (circled in red):
   
   You should have this result:
   
3. Repeat the last step, using the following settings this time:
   
   It should be looking something like this now:
   
4. Do the same stroke one more time, now with these settings:
   
   And there it is. Notice how the inner strokes are not perfectly round. If you use smaller stroke sizes, the circles will be round.
   
5. Now that we've had some fun stroking together, let's try out a pattern fill trick. First, make a black square:
   
6. Use the magic wand tool to select the square
   
7. Go to 'edit > fill' in the top menu and select 'pattern'
   
   Choose this pattern:
   
   To get this:
   
8. Go to 'edit > fill' again, this time select the following pattern:
   
   Now set the opacity to 50%:
   
9. The final result: