Rabbi Yehoshua (Pirke Avot 2:16) said that three things removed an individual from this world: an evil eye, an evil inclination, and baseless hatred of others. The latter two are relatively self-explanatory, but what is an evil eye (עין הרע)? Evidently, it's not some gigantic eyeball with supernatural powers that causes the world's problems. Although given the superstition surrounding the evil eye, that is a pretty good metaphorical representation. The notion of an evil eye is one of the most universal superstitions out there, and the Jewish people were not exempt from this superstitious belief. The evil eye was the supposed power that a malevolent stare can bewitch or harm another. To try to ward of the evil eye, certain Jews took on the practice of amulets, whether that was in the form of blue beads, the red string, or the chamsa (חמסה). Aside from my issue of using objects as amulets, the superstition misses the point of עין הרע.
The commentators have various opinions of what עין הרע is. R. Yonah opines that עין הרע refers to jealousy. One who is constantly envious is spiritually destitute because one can hardly appreciate what he has. As Ben Yoma points out (Pirke Avot 4:1), "Who is happy? He who is satisfied with his own lot." Not only is there a lack of appreciation for one's lot, but there is also a propensity to undermine another's wealth and prestige in hopes that they can be nefariously acquired. The insatiable desire to go after another's wealth damages both oneself and those around the individual. It is so powerful that it ended up being the last of the Ten Commandments (Exodus 20:14). Avot de Rabbi Natan viewed this jealousy in more spiritual terms. One with the עין הרע will not want his friends to be successful in Torah study. Maimonides viewed the עין הרע from the standpoint of stinginess. If one is stingy, one is constantly obsessed with material wealth. With this worry, one can never really enjoy life since they are in constant fear of being in poverty. Additionally, Hillel said in Pirke Avot 2:8 that "the more flesh, the more worms," i.e., overindulgence in materialism is detrimental to spirituality.
Although there are some variations of opinion, the general consensus is that עין הרע is an issue of jealousy. The underlying point of עין הרע is that עין הרע is an internal phenomenon, not an external one. It's easier to blame some external force for our shortcomings because it means that we don't have to confront them. The Sages were wise enough to realize that having an עין הרע was a detriment, which is why having a good eye (עין טובה) was praiseworthy (Pirke Avot 2:13). How do we go about developing this good eye?
One response is gratitude. There is a huge correlation, and dare I say causation, between gratitude and happiness. If you do not have a sense of gratitude for what you have, your eye wanders towards what others have. R. Yonah (commentary to Pirke Avot 2:13) said that a good eye was someone with a charitable and benevolent attitude towards others. Benevolence is more than a feeling; it needs to be acted upon in order to matter. Whether it is צדקה ("charity") or גמילות חסדים (acts of loving-kindness), it is a matter of externalizing the sentiment in order for it to come to full fruition, much like with happiness. If I am to be so bold as to add my own commentary, I would opine that a change in perspective would help. What I refer to is the idea that we are not in competition with one another; it's not zero-sum. Certainly when it comes to spirituality, G-d does not derive any pleasure from oneupmanship. There is no point in oneupmanship because we are all created in His Image, and G-d expects us all to act ethically. G-d does not want us to knock others down. G-d wants us to wish other people the best in life, and to be able to help others in whatever capacity possible. Being able to help and give to others, not to mention realizing the good in our lives, is the best antidote to eradicating the evil eye from our midst.