There are many ways to draw grapefruit. Here's a simple way to draw grapefruit:

Draw an oval grapefruit. Note that the bottom of grapefruit is wider than the top, so it looks more like the shape of grapefruit.

Draw an arc on the top of grapefruit to represent the skin of grapefruit.

Draw some arcs at the bottom of grapefruit to show the texture of grapefruit.

Painting grapefruit with dark pigments and paying attention to the change of color depth can make grapefruit look more stereoscopic.

Draw the highlights of grapefruit with light pigments to make it look more shiny.