You can draw anything at all and it can be very very quick, less than a minute, or as slow as you wish.The objective is to make a drawing a day for month.
To start, try drawing your feet, like this beautiful study here by Leonardo da Vinci... not into feet?...sketch a tree, a view from the train, a song....use your visual journal notebook and date each journal entry.
Once you get in the habit you may find you are making more than one drawing a day.
Suggestions for drawing subjects
People in your family, they don't need to pose, make a quick sketch of someone doing something.
People in the park or in public spaces
Pets
Furniture
People on furniture
View from a window
A tree or plant or flower
Your shoes, your bare feet.
Yourself in the mirror
Your friends
A still life, objects on a table.
Your breakfast, or lunch
Cartons, containers, wrappers
Drawing from TV
Drawing of another artwork (be sure to cite the original)
Drawing from the news
Drawing from imagination
Artist Links... there are so many artists who incorporate draw as a daily practice, here's a few to explore
Vija Celmins-delicate hyper-real pencil renderings of skies, sea, desert...long sustained drawing
William Kentridge- bold charcoal drawings and animations
David Hockney on drawing from life
Why you should keep a daily sketchbook - article on artsy
Find some good drawing suggestions on drawpaint academy