1- Draw a circle and divide it into two halves.

2- Draw another circle of the same size based on the mid line of the first one.

3- Draw the tail.

4- Now connect all what you draw like that...

5- Now draw the out line of Nemo... add some thickness at the sides of his face as his cheeks.

6- Now draw 2 innocent big eyes.

7- Add the white stripes on the body like that.

8- Draw his smile.

9- Draw his fins.... and don't forget his lucky fin.

10- Remove the pencil marks.

11- Add some shadows and stripes for the fins.

12- I colored it and added some shadows because Nemo is a 3D character.
Enjoy Drawing