My daughter decided to do a 365 photos in 2013 self-challenge, and I decided to join her. Here's my first dozen days posted on Flickr. (Click on the square images to see the full photos at Flickr.) Hopefully we'll be able to sustain our efforts.
I found it hard to do a themed photo-a-day challenge on Instagram. Maybe you will have an easier time of it, especially since you are free from a theme?