White eyeliner is the secret...
Use white pencil to line the inside rim of your lower eyelid. This will reflect the effect of a bigger white area of your eyeballs!
White pencil works for almost all sets of eyes, but If your eyes are a close set, use the white pencil to lightly line the section where the upper and lower lids come together, closest to the nose.
This will make them appear wider apart. The key is to pop those eyes out.
Here is a video tutorial about white eyeliner.
Source: NewBeauty Magazine