Drawing freehand circles is A Very Good Way of practicing your drawing and painting skills.
Skies are a set of abstract shapes and they often cause learners consternation. The reason I believe is that most people like to paint something real, not something that is really abstract. Also there is a timeframe to painting a sky. An abstract sky usually takes me about two days to complete: you cannot compare an abstract sky to one that is a flat wash or graded wash. So when you paint a sky with lots of different shapes and curves move your mind away from realism into the realm of the unknown.
This particular painting involves using a range of watercolour skills: wet on wet (sky), glazing (silhouette) colour mixing, different brushstrokes. You need to make a very definite drawing of the tree structures so you do not obliterate them with your washes.
The main technique to use, apart from those I have mentioned above is Tonal Skill. This is where the cloud shapes have a range of tones on them to make them look 3D and moving. This Takes Some Time. Do not think you can complete this is a two hour painting session.
The semi circular shape should remain the colour of the paper with a little crescent of yellow surrounding the shape to give it some 3D effect. With the dark silhouette so close to the shape the principal of light against dark is evident. When you have finished this painting consider all the techniques you have used and also consider all the fine ingredients that make a painting worthy of framing and displaying.