For as far back as I can remember, my parents would always admonish me and my siblings to keep good company. My Dad specially had a favorite saying, "Show me your friends and I'll tell you who you are." Needless to say, I was always very conscious, and careful about choosing the right people to surround myself with. In Islam it is doubly true and essential to surround yourself with righteous companions, because they will help to keep your feet planted on the straight path, while doing otherwise may lead you astray.
It was Ahmad ibn Harb, rahimahullaah, who said, "There is nothing more beneficial to a Muslim's heart than to mix with the righteous and to watch their actions, while nothing is more harmful to the heart of the Muslim than mixing with sinners, and watching their actions." No matter who you are, or how strong or independent you may feel, no man, or woman, is an island, and you can't make it through this life alone. This is why Islam so stresses the Jama'ah, or the congregation.
The sayings that there is strength in numbers and that it is the lone sheep that gets devoured by the wolf are true. Therefore we need to adopt correct manners, in that we try ardently never to do an action or to befriend anyone without knowing whether the pleasure of Allah is in it or not, and never loving and hating for worldly reasons. For the Prophet of Allah, sallallahu alayhi wassalaam said, "Whoever loves for Allah, and hates for Allah, gives for Allah and withholds for Allah, has completed his faith." (Abu Dawud) So who should be our companions? First of all they should be good Muslims, who believe in Allah and His Messenger. For Allah says in the Qur'an, "And who so obeys Allah and the Messenger [Muhammad, sallallahu alayhe wassalaam], then they will be in the company of those on whom Allah has bestowed His Grace, of the prophets, the Siddiqun (those followers of the prophets who were first and foremost to believe in them), the martyrs, and the righteous. And how excellent these companions are." [4:69]
Secondly, being around them should make you want to increase in good deeds. Allah ta'ala says, "And We have sent down to you [O Muhammad, sallallahu alayhe wasallam], the Book [this Qur'an] in truth, confirming the Scriptures that came before it and Mohayminan [trustworthy in highness and a witness] over it. So judge between them by what Allah has revealed, and follow not their vain desires, diverging away from the truth that has come to you. To each among you, We have prescribed a law and a clear way. If Allah willed, He would have made you one nation, but that [He] may test you in what He has given you; so strive as in a race in good deeds. The return of you [all] is to Allah; then He will inform you about that in which you used to differ." [5:48]
By aligning ourselves with people who do good deeds, we are then prompted to compete with them in this regard, and thus improving the character and the religion of everyone involved.
Lastly, but by no means the least, our companions should help us to remember Allah. For Allah Ta'ala says, "O you who believe! Let not your properties or your children divert you from the remembrance of Allah. And whosoever does this, then they are the losers." [63:9] In this time of hustle and bustle, it is very easy for us to get caught up in the pursuit of worldly gains. This is why it is increasingly important to surround ourselves with people, who will encourage us to think of Allah, in every instance of our lives. The superiority of the remembrance of Allah was explained by the Prophet Muhammad, sallallahu alayhe wasallam, who said, "The example of the one who remembers his Lord, in comparison to the one who does not remember his Lord, is that of a living creature compared to a dead one. (Bukhari)
So let us take stock of the people we spend our time with. Do they fall into the above categories? If our friends aren't doing these things, then what does being with them say about us? We should strive to love those who love Allah, and to hate those who hate Allah, and what He has sent down of guidance for humanity. For the Prophet, sallallahu alayhe wasallam said, "Whoever possesses three things will find the sweetness of eman. For Allah and His Messenger to be more beloved to him than anything else; to love a person for Allah's sake alone; and to hate to return to disbelief the way he hates to be thrown into the fire." (Bukhari)