Next, add the eyes. Press SHIFT + A and select Mesh > UV Sphere. There are two different types of spheres, UV and Ico. The only difference is how the vertices are laid out by default. A UV sphere has concentric rings that go all the way around it, which works really well for eyes because you have a pupil which is a circle inside of the eye which is another circle.

Once you've added the body move the body, move it so it's centered on the eye, then rotate the body so it's roughly in line with where the eye is angled. Do this in object mode. You are modifying the object's location, so X will be sideways relative to the eye, not to the world. Press TAB to enter edit mode and then scale along local Y. To do that, press Y twice. Pressing Y once would scale in global Y, but Y twice will scale along the Y of the eye, which has been rotated. Also scale it along X an Z to get it the right shape, then move it up to it sits out front of the main body.

In edit mode, hold down ALT to select a ring around the pupil, and everything inside it. Once it is selected, press P and choose Selection. This will split the pupil out into its own mesh so it can be printed separately. With the main eye shape done, press SHIFT + D to duplicate the eye to make the other one. Move it into position with G.

Because we are using 2.8. we can edit multiple meshes at the same time. You couldn't do this with previous versions. Edit the pupils. Select everything with A, then hit E to extrude. That will let you pull the newly extruded vertices down into the eyeballs. Once they are pulled in, press S to scale, then 0. That will make them nice and flat so they don't have any curvature.

Do the exact same thing with the eyes themselves. Edit the eyes. Select around the edge where the pupils are by holding ALT, then press E to extrude. You will want to enable vertex snapping at the top of the window. This will let you snap to the bottom of the pupil, making sure the two line up nicely. Press G + Z to move the newly extruded edge down in Z, and mouse-over the bottom of a pupil. The edge will snap to that depth. Once the edge is at the correct depth, change your Transform Pivot Point to Individual Origins. Hit E again then scale (S) and 0 to close off the bottoms. As usual, remove duplicated by distance.

Select one piece of the eyes and add an Edge Split modifier and a Subdivision Surface modifier. That will make nice sharp edges and add geometry. This won't add those modifiers to all pieces of the eye though. Select all of the other bodies that you want to have the same set of modifiers and make sure to select the body you already setup last. That makes it the active element. Now you can press CTRL + L, which will link any features of the active element to the other bodies. Select Modifiers. This will set up all of the other bodies to have the same set of modifiers that the Active Body does. This is an easy way to apply multiple modifiers to multiple bodies