Here is my simple tip...
1) Make a rough selection around an eye with the selection tool (or tool of your choice)
2) With the eye still selected, hit Ctrl-J to put the eye on its own layer
3) Change the mode to screen for the new layer just created
4) Lower the opacity to your liking - probably around 30%-40%.
5) Erase any extra area around the eye. The better your selection, the least you have to erase. I am lazy so I erase (using a layer mask) after the fact.
6) Repeat for the other eye.
This technique (along with others) was applied to this image.
Note that eyes shouldn't be WHITE like many people do in their post processing. Brighter yes, white no. So adjust the opacity to your liking.