As summarized by Channie Koplowitz Stein.
We often hear the expression, or we ourselves often use it: bli ayin hora, "without (the influence of) the evil eye." 
The Torah tells us that Joseph was extremely handsome, handsome "to raise one's eyes to."
The concept of an evil eye is enigmatic, yet it produces a sense of uneasiness and even fear within us. But we are told that through the blessing Jacob gave Joseph and his descendants before his death, saying that they would be as fish under the sea, invisible to the ill will of others, Joseph would not be affected by the evil eye, according to Rashi's explanation. What trait did Jacob see in Joseph that prompted this unique blessing?
The Torah tells us that Joseph was extremely handsome, handsome "to raise one's eyes to." That simple phrase lies at the core of the blessing Joseph received and, by extension, we can receive through him and learn from him. Although Joseph had an unusually beautiful physical form, he never believed that this was a personal accomplishment, and he never allowed it to sway his eyes from the appropriate path.
The most telling incident occurs when Potiphar's wife tries to seduce him. Joseph's rejection of her advances contains the two elements that reveal the mindset capable of repelling the evil eye. First, Joseph highlights that she belongs to another and therefore he has no right to take her. Then he acknowledges the centrality of the Lord in his life, and he refuses to sin. These two steps form the basis of a life which will both accept whatever one has with a good eye, and see others and what they have with a good eye without envy.
As the Maaseh Rokem points out, the "evil eye" can come into play only when there is a sense of negative wonder at what exists. This wonder expresses itself as questioning the correctness of something good without attributing it to the Creator of all good. For example, one might exclaim, "What a beautiful baby," totally without malice. However, the appropriate response is looking upward and saying, Boruch HaShem, "thanks to HaShem", thereby attributing the blessing of that beautiful baby to its Source, to Hakodosh Boruch Hu. If one begins having a sense of personal pride, he opens the way for the angels to question HaShem's judgment, so to speak, in bestowing such blessings on someone who doesn't appreciate them as gifts from the Creator.
Throughout his life, Joseph attributed everything to HaShem, whether he was in prison, in Pharaoh's court, or the supreme ruler of all Egypt meeting his fearful brothers. He attributed whatever skills he had to the One who endowed him with these skills and these circumstances, and used them all in the service of HaShem.
Joseph learned this attitude from his father Jacob. Jacob stood in stark contrast to his brother Esau, one with an evil eye. When Esau, with 400 (armed) men, approaches Jacob, he actually wants to cast an evil eye on Jacob and on his descendants. As Areset Sefasainu points out, ayin ra, "evil eye", equals 400 in numerology. In their initial dialogue, Esau raises his malevolent eye and asks, "Who are these children to you?" Jacob thwarts Esau's intention by immediately attributing his beautiful family to the grace and the blessings of HaShem rather than claiming them as totally his own. He further maintains that he has "everything", while Esau claims he has "much".
Bilaam, the evil prophet, tries to use similar tactics. He too raises his eyes malevolently, but when he sees the camp of the Israelites, his goal is thwarted, and, instead of cursing the Israelites, he is forced to bless them. What was it in these "goodly tents" that had the power to negate such evil intentions? Certainly, no doorway faced another, but within that sense of privacy was an even greater sense of contentment that each family felt 
Bilaam, the evil prophet, tries to use similar tactics.
with what was given to them. They felt no need to look into their neighbors' homes, perhaps become jealous and covet something which was not theirs. The positioning of their tents testified to their contentment and satisfaction with whatever HaShem had allotted to them, to the fact that they felt they had everything.
Just as the generation of the desert was able to thwart the power of the evil eye, so too do we have that same power. We, too, must maintain a deep connection with and gratitude to Hakodosh Boruch Hu, and must acknowledge that all that we have is really all that we need. It is only when we look at the Joneses and their possessions that we feel we must keep up with them.
When we have this approach to life and what HaShem offers us, we are ready to take our vision to another, higher level. We are ready to transform our eye from one that sees the world from an egotistical point of view, from one that begrudges others their good fortune if we have less, to a "good eye", an eye that can rejoice with others in their good fortune, whether it is in material wealth, family development, social standing or spiritual growth. We can even use our eyes to look so kindly at others that we actually bestow blessings upon them.
This was the process of the Levites, and most specifically the priests, who convey God's blessings to us to this day.
When the riches of the Egyptians who drowned in the Red Sea washed up on the shore, the Israelites were granted them as payment for their two centuries of servitude. The Levites asked Moses if they were entitled to take from the booty as well, since they were never enslaved. Moses answered them that they could take from the booty, since they were emotionally enslaved with their brethren even if they were not physically enslaved. However, the Levites were not selfish, with restricted vision. They were happy that their brethren could finally get compensated for their labor and they felt no need to share in this largesse. Because of this ability to look kindly and happily at others and at what they had without wanting even a part of it, says the Shaarei Chayim, they merited to be the vehicle for HaShem's blessings for Bnei Yisroel.
Seeing, then, is not only a passive activity. It is also active. It can shower blessings on whatever and whomever falls under its gaze. In fact, during creation, when HaShem "saw" that His work was good, as Rabbi Goldwicht explains, He infused in His work an energy, a life force, upon which all that He made became "very good."
Although Man is influenced by what he sees, the reverse is also true. Man influences and puts his stamp upon that which he sees. So when HaShem promised Jacob that Joseph would "place his hand upon your eyes", the implication was that Joseph, who was not influenced by what his eyes saw around him, would exert his sanctifying influence on Bnei Yisroel, who were now descending to Egypt.
Each of us has this ability.
This gift of benevolent sight was the gift that HaShem also gave Moses. Although it was preordained that Moses would not enter the Promised Land, HaShem nevertheless let him ascend the mountain and look down upon all that good land and exert his influential blessing with his eyes on the land and on its future inhabitants, whom Moses had led so selflessly.
Each of us has this ability to acknowledge that all we have is a complete blessing from HaShem, that we indeed have all we need. Then we can look kindly and warmly on all others and on the world around us, so that all will feel blessed and warm in our midst, just as we feel the blessings of HaShem's gaze when He shines His face upon us. Armed with the weapon of a "good eye", we will not be subject to the malevolence that an "evil eye" can elicit in strict judgment from Heaven.