How can I select suitable leaves for hammered leaf art? Over the summer I tried to do some hammered leaf art. Since I had never done it before I was just grabbing random leaves and plants that I thought would look good if I beat them on some watercolour paper. 



I thought a fern and some maple leaves would look really good but alas I has awful results. You can't really see where they were because there was not enough juice in them. 

The leaf in the upper left looked really good. After reading my first intro to this art the author said that: 


  You're looking for things with bright colors that aren't too juicy or too dry. It'll take a little trial and error to find good plants, so grab a variety and play around.


Is that really the only advice when getting into this... trial and error? I understand crafting has a large part of just that but in this case is there more to go on for this when it comes to select leaves to hammer?


If I find a good leaf can I assume that species of that size and age is a good choice going forward?
Is there a way I can tell visually if a leaf is juicy or dry?


How can I effectively access a leaf/plant for use in my nature prints or hammered art?
My wife and I did a bit of this the last time we were in Japan. It was very difficult, but also very interesting. 

As the previous answer indicated, experimentation is key here. In fact, I almost think it's the whole point of this technique. Each time you fail miserably, you'll learn a bit more about what doesn't work. 

Try everything you come across (it's all free materials anyway). Make notes on what did/didn't work. You can number your papers to correlate with your notes.

You may find that different plant materials respond better under different hammering techniques.

Once you have developed a feel for it (through experience), you will quickly develop your own signature style.

Don't be afraid to fail miserably.