If you’ve never played with watercolor before and you want some very simple and basic exercises, I would recommend trying to replicate the brush marks below, as seen in the 1905 book Brush Drawing, by May Mallam.
Holding your brush
You can see here that the orientation in which you hold your brush can affect the stroke that you are able to get. Hold your brush more at a slant, and you will be able to easily vary the weight of your line. If you hold the brush upright with just its tip to the paper, you can get a finer line.
Practice creating patterns by just fitting simple brush strokes together in different combinations.
Practice some strokes where you bend the line in different directions. I would suggest literally replicating this page for practice.
Try coming up with some of your own line combinations.
What direction is the light coming from?
These examples show objects painted in a very simple shaded manner. The lightest areas, the highlights, are where the light is shining, and the dark areas are on the opposite side to where the light is shining.
It is often helpful, especially when you are painting an object, to establish which side is the highlight and which is the shadow. These illustrations also depict the shadow that the object is casting on the ground.
This book also has some very helpful directions and hints on painting floral shapes in color. Here is an example of how you can simplify floral shapes into smaller pieces and how they fit together into the whole flower.
I am always doing that which I cannot do, in order that I may learn how to do it.