While the earpods have been designed to fit a variety of ears, I still find mine a little loose. Being a Sugru nut, here is a step by step on how to add a silicone rubber layer to your earpods to make them fit better on your ears.
Step 1: Getting Started
Once you get your paws on a small pack of Sugru, go ahead to open it. You only need a little per side (roughly 1/5, 1/6 of the pack).
Go ahead and peel some off, knead it a bit, and roll it down into a rod roughly based on the picture here. An EarPod is next to it for estimation.
Step 2: Sugru - first wrap
Roll the Sugru around the Earpod. You need to avoid any of the holes on the EarPods. I found that it is best to wrap it first at an angle (see pictures) which avoids all of the ports first, so that you can adjust as you press down on the sugru later.
Step 3: Sugru - Press down
Carefully now, press down on the Sugru, coating the EarPods. You want a layer that we can customize later, but not too thick. You can see that I have two different ways of coating.
As before, make sure the ports are not obstructed.
Step 4: And now, the custom fit
Sugru takes about 30 minutes to reach a 'touch-able' state. You should now be able to fit the EarPods in your ear, applying gentle pressure, to customize each EarPod to the shape of your ears.