Then there's this idea, which could be done with any medium.
That project is in a chapter called "Design" which has some great ideas for ways to start looking at the world as an artist. It also suggests some exercises that gets the reader practicing making images more abstract, distilling them to their cores. All of the is written in this oddly formal, passive voice, so I'll try to distill the basic messages at the end.
A few excerpts:
"Try out the following exercise. Look closely at the leaves of a tree, noting the outside shape and the pattern of the veining within that shape; touch and appreciate the texture of the bark; study the changes of colour within an area. Now make a small sampler in any medium to bring out the character of some aspect of the tree which you have observed. Repeat the exercise with a stone, noting its overall shape, whether the surface is smooth or pitted like a crater. Find a suitable technique in which to convey your impressions. Man-made objects, too, can serve as a starting point for design: for instance a wrought iron gate, the pattern of tiles on a roof or windows on a wall. The main thing is to always be aware of one's surroundings, making mental notes to be filed away for future reference."
"After an object has been looked at and touched, an attempt should be made to transfer the experience to paper (ie to make a design based on impressions gained while handling the object). This will not be easy at first, but a start can be made in quite a simple way and confidence will grow with practice.
"Start by basing a design on the veining in a stone or the grain in a piece of wood. Although it may seem alarming at first, make the drawing boldly, say with a felt tip pen on a large piece of paper. Start in the centre of the paper with one firm, unbroken line. If this proves to be incorrect resist the temptation to start again, and put in the next line, and the next, until the drawing is complete. The original piece of wood or stone serve only as a starting point and need not be copied slavishly. Keep your mind open to any chance effects which may be produced and learn to make use of them. [...] As a more advanced exercise take, for example, a thistle, and try to convey in stitches not the actual appearance of the thistle, but the prickly feeling which it suggests. This will entail finding the right materials and searching for the most expressive stitches to convey the prickly sensation."
A simplified version of the above: Look at and touch a chosen object such as a leaf, or a stone. Examine the texture, colors, surface, patterns. Make a piece of artwork (in any medium: drawing, painting, collage, etc.) depicting one aspect of your object. Next, after further studying the object, draw it in marker using big, bold lines. Finish the drawing even if you feel like you've messed it up. The key point is to treat the object as just a starting off point; don't try to faithfully reproduce it .
I like how the patterns the author comes up with are so Zentangle-ish:
There aren't any images given to accompany this activity, so I chose a couple of inspiring images that could, conceivably, be the end result: