In the center of the image, the mermaid sits comfortably on a smooth rock. She wears a delicate seashell bra and has matching seashell hair accessories tucked into her flowing hair. Her long tail curves around the rock, showing off individual scales that are perfect for adding different shades of color. These focal points draw the eye and provide a great space for shading.

Around the base of the rock, you will find several different types of seaweed swaying in the current. A few starfish and scattered seashells rest on the sandy floor nearby, adding texture to the ocean floor. In the background, a small school of fish swims together through a stream of tiny bubbles that rise toward the surface of the water, creating a sense of depth in the cartoon scene.

For the mermaid's tail, try using a gradient technique by blending two or three similar colors like teal, emerald, and mint green. You can use a metallic or glitter pen for the scales to give them a shimmering look that mimics the way light hits water. The seashell bra and hair pieces look lovely in soft pastels like lavender or pearl pink to make them stand out against her skin and hair.

The seaweed can be various shades of green or even deep reds and browns to create contrast against the blue water. Since this is a whimsical scene, feel free to use bright, bold colors for the small fish and starfish. Lighter blues or even a very pale silver work well for the bubbles to make them appear translucent and light. Using a light touch with your pencils can help keep the bubbles looking airy.