I have some experience dehydrating fruits and vegetables and a little meat.  

My advice for a beginner is start with apples.  They are cheep and easy.  Slice them one way and they are soft and chewy.  Slice them another way and they will be crunchy.  (I like Granny smith’s crunchy style.)

Nectarines were good.
Plums were not good.
Watermelon gets a consistency of cotton candy.
I need to try peaches again.  The one I tried was not good when I started with it.