I see inspiration here, from all the talented contributors ("experts" and beginners, alike!). I also try to look for small motifs and colours, shapes and sizes that can be easily translated to cookies. it never has to be perfect! A lot of the time, I doodle on paper, and that's where some design inpiration comes from. Colours mostly. I use markers and just draw like when I was a kid. You'd be surprised what happens!
Just go with your gut. It's all good!