Photoshop Trees, ugggggggg!

When I first started using Photoshop, the trees were always the most difficult. After some time struggling with it, it got easier, but you need to know a couple of tricks to really have realistic trees in your drawings. Below is a link to a great basic tutorial on how to make the trees in your drawings look much better. 

http://www.phong.com/tutorials/mask.tree/

Let me know what you think. What other Photoshop tutorials have you found that make your drawings better?