This loose lively painting of sunflowers will benefit from a swift application of color, so be prepared to work quickly. You can give yourself more time by mixing up your colors in advance and keeping them in separate wells in your palette.
Mix a rich mid-green from 70% New Gamboge and 30% Ultramarine. This should be a weak tea consistency, i.e. thin enough to form small beads of color. For the seeds in the center of the flower mix a warm dark neutral of cream consistency from Burnt Umber and a little Ultramarine.
With your paper tilted at approximately 30 degrees, start by taking the larger round brush and painting three sunflower heads with New Gamboge, which is a rich warm biased yellow. Don’t worry about painting each individual flower petal, just get the overall shape. I’m using a synthetic haired brush which has a springy quality to it that I find works well for these types of shapes.