Draw a small oval or rounded rectangle for the main body
Add a slightly curved line across the top for the mouse shape
Draw a vertical line near the top center for the scroll wheel
Add a small circle or narrow oval for the scroll wheel
Draw a line down the middle from the top to the bottom for the left and right buttons
Add a short cord extending from the top if drawing a wired mouse
Round the bottom edges to make the base smooth
Add a small shadow or outline to finish the shape