I've always been a fan of painting and drawing exercises to loosen up my work. This is a technique I've hit upon to look at some colours other than my usual palette (greens & blues if you hadn't noticed!) and also improve my pen and ink line work.
I use Kuretake Gansai Tambi watercolour paints for these exercises, they have lovely pigment intense vibrant colours that seem to reflect nature. I've deliberately kept the pictures in a hardbound Daler & Rowney A5 watercolour sketchbook, this way they just stay as sketches and there is no pressure to create finished artwork - just 15 minute exercises.
I used my (very old) Rotring ArtPen - which has a lovely drawing nib. I have just converted it to use with waterproof ink, by filling an old cartridge with De Atramentis black document ink, so far this is working well, no clogging and I can draw under and over watercolour paint without any smudging.
To create this sketch I took my sketchbook and paints out into the garden and sat next to an orange tree, I soaked the surface of the paper with clean water and then painted orange and green 'splodges' wet in wet onto the paper, allowing the paint pools to move and bump into each other in happy accidents. Its not entirely abstract as I was deliberately trying to make round orange shapes and elongated strokes for the leaves, but abstract enough for my purposes.
I let the paint dry thoroughly before inking, and took a few reference photos in the garden to use as a basis for the line work, though of course I had to make the composition of the oranges and leaves up as I went along determined by the colours on the page, which is the drawing part of the exercise.