Examples of outline:

◆ First

▹Before you start, please make sure that your brush in the hard brush. If you want it thick, increase the size.

◆ Second

▹Click on that red box I'm showing  

◆ Third

▹Click on the new layer and trace it!

◆ TIPS:

▹ You don't have to make it perfect. 

◆ Fourth

▹ Choose your outline colour. I mostly use white.  

◆ Fifth

▹Once you're done tracing, right-click and this will pop out. click on stroke path.

◆ Sixth

▹this will pop up and choose 'Brush' and click OK.

  ▹And you're done!  

Credit: http://ravenorlov.deviantart.com/

I used my own PNGs and PSDs.

Thanks for reading!