Step 1 Sketch
Start the sketch by drawing a circle. Then fill the circle with leaves, plants, flowers, text and anything else you would like to have in your illustration. Instead of filling the circle, you can also arrange the elements as a wreath.
Tip: Start with the largest elements and fill the empty spaces with a small, fine element at the end. For example, dots or single leaves.
Step 2 Colours
Now make a new layer. Paint the basic colours on this layer. Paint all plants/flowers of the same species in the same colour. Make sure that you use lighter and darker, colder and warmer, pure and impure colours to create a harmonious colour scheme.

Step 3 Shadows and Highlights
You can either continue working with Alphalock and the base colour layer or create a new layer that is a clipping mask above the base colour layer. Add shadow highlights, slightly different tones until you are satisfied.
Step 4 Final touch
Finally, you can add a shadow to the leaves and flowers. And my personal tip is to add a grain.