On Shavuos Klal Yisrael received the Aseres Ha'dibros; a veritable formula for self perfection. The Aseres Ha'dibros begin with "Anochi Hashem" and end with "Lo sachmod" - do not desire anything which belongs to another, and as Rav Wolbe points out, there is a direct correlation between these two commandments. (Da'as Shlomo, Zman Matan Toraseinu pg. 477)
The Ibn Ezra (Shemos 20, 14) cites the obvious question. How can we be commanded "not to desire?" How can a person possibly not desire a beautiful item that belongs to someone else? The Ibn Ezra answers with a parable. A peasant who beholds a princess will not even entertain a thought of marrying her because he knows that it is absolutely impossible. Likewise, a person must know that a beautiful wife or affluence is not bestowed upon a person as a result of his brains or his brawn. Rather, everything is decided and allotted by Hashem. One must realize that because the Torah forbids his friend's wife to him, the possibility of marrying her is more remote than the possibility of the peasant marrying the princess.
The question posed was a difficult one: How is one capable of ensuring that the feelings of desire do not even arise in his heart? The answer, says the Ibn Ezra, is to appreciate the impossibility of the desire coming to fruition. When one comes to this realization, the desire will not even cross his mind nor enter his heart. How does one come to such a realization? This is achieved by inculcating the idea of Hashgacha Pratis, as the Ibn Ezra continues:
"Therefore, he will be happy with his lot and his heart will not desire that which is not his, because he knows that Hashem did not want to give it to him and he cannot take it by force or through schemes. Therefore, he should place his trust in his Creator that He will sustain him and do what is best in His eyes."
The simple explanation of how to fulfill the mitzvah of "Lo Sachmod" is to be happy with one's lot and to trust Hashem that He is doing what is truly best for him. This, in effect, is the first mitzvah of the Aseres Ha'dibros; "I am Hashem who took you out of Mitzrayim." This is a declaration which encompasses all aspects of Divine Providence. Yetzias Mitzrayim was the ultimate demonstration of Hashem's involvement in all aspects of everyone's lives.
How does a person know if he has properly fulfilled the first commandment? He can gauge his success when given the opportunity to fulfill the last of the commandments. Does he desire his neighbor's wife, car or house, or is he entirely content with what Hashem has allotted him?
Shavuos is the time to strengthen our commitment to what we accepted many years ago on Har Sinai. The Rikanti writes that "Lo Sachmod" is the root of all the mitzvos. In light of what is written above this is quite understandable because this mitzvah's fulfillment is contingent on our emunah and bitachon in Hashem which is the root of the entire Torah. Strengthening our emunah will in turn aid our fulfillment of Lo Sachmod and intensify our performance of all the mitzvos, and ultimately it will bring us to the self perfection intended by the Giver of the Torah!
Good Yom Tov!