I did this quick little study of grapes as a demo for my pastel students. Grapes are one of the most complex subjects to draw or paint. If you think of them as masses, rather than individually you will get much better results.
Start by massing in the entire bunch of grapes, don’t draw individual globes, block in the shadows. From there, begin carving out those grapes which are the most prominent, these you can begin to add some details to. Remember that not every grape needs to be done in fine detail, keep the ones in the shadows and the ones at the bottom of the bunch subdued and just suggested.
Use a lot of color variation, grapes are translucent and have many colors in their skins: red grapes have blues, yellow ochres, greens and purples in them. The highlights should be handled in a way that includes both warms and cools and some that are prominent vs. others that are not as vibrant.
This is a good exercise in observation, drawing complex subjects helps to train your eye in reducing things down to basic shapes, as well as to better see a wide range of values and unexpected colors.