I am always flattered when asked where I come up with all these ideas for paper art. My answer is much like Stella's, "I've always depended on the kindness of strangers." I get the majority of my ideas from online resources and I credit them whenever possible in my workshops, web site tutorials, and in my former newsletter.
Take the waterfall card for example, I was introduced to this card by Split Coast Stampers http://www.splitcoaststampers.com/resources/ and taught it as a stamped card around 2003-2004. This year I revised the design to include die cuts from the Wizard http://www.spellbinders.us and now it's making another round. Pine Cone Press just featured one in their latest book too http://www.pineconepressbookclub.com/
You don't have to think of everything yourself, you just have to start making art. Enjoy!
Pictured in this blog--two stamped waterfalls and one with die cuts, the design is orignal to me, but the idea---well that came from one of many cool resources.