For instance, on the day I sketched this dragonfly, I had revisited the old deck of Medicine Cards I hadn't seen in years and blindly selected the Dragonfly card. Oh, I've always been intending on drawing a dragonfly and that day was as good a day as any!

One recent morning I noticed beautiful morning light streaming into the kitchen counter so I grabbed some berries from the refrigerator and took some photos of them in that light (because I knew the light would be gone before I could paint it). The berries cast wonderfully long shadows. I wanted to play with painting shadows in watercolor, and this gave me the opportunity.

And if I'm at a loss, I search out my own collection of photos, or I look online at places like morgueFile, Paint My Photo, or Wikimedia Commons (to avoid copyright infringement) for photos that tweak my interest and sketch those.
It helps to have on-going projects. I am working on some "retrospective" trip journals, sketching photos from past trips I did before I got into sketching. It's a great way to reminisce about wonderful trips you've taken.
I also am in an Artist Trading Card exchange project with fellow artists, and I use my Artist's Journal to explore certain ideas first.

There are so many ways you can keep motivated for a daily art practice, whether in you Artist's Journal or in other journals and art projects too! I hope you have some ideas and inspiration for your own daily art practice!