Praise be to Allah, The Almighty, Who created man in a balanced form. He inspired and adorned him with the beautifying light of faith and taught him eloquence and made him a pioneer and superior being, providing him with a tongue to articulate what is in his heart.

Truly, from among the greatest blessings of Allah, The Almighty, the tongue, is one of His most sophisticated and unique creation of all organs in the body. Although small in size, its impact is paramount. Faith and disbelief, which stem from obedience and disobedience, respectively, cannot be known except through the testimony of this very organ.

Moreover, those who keep their tongues unchecked, fall prey to the devil’s influence, who causes them to say evil things, and leads them to an edge of a bank that is about to collapse, forcing them to fall down. Truly, no one escapes the evil of the tongue except those who restrict it to the constraints of Sharee'ah, using it only to utter what is beneficial for them in this life and the Hereafter, while preventing it from uttering anything that may bring any harm, sooner or later.

In Usul al-Kafi, it is narrated, “Preserve your tongue from idle talk, because the majority of the sins committed by the son of Adam is due to the tongue only. No other part of the body commits more sins than the tongue.”

Rasulullah salallahu 'alayhi wa sallam also remind us the important to be allways carefull with the use of the tongue as mentioned in Hadits below

Abu Hurairah (radiallahu anh) reported: The Prophet (salallahu 'alayhi wa sallam) said, "He who believes in Allah and the Last Day must either speak good or remain silent.''
[Muslim]

Sufyan bin `Abdullah (radiallahu anh) reported: I asked: "O Messenger of Allah! Tell me, of something to which I may remain steadfast.'' He (salallahu 'alayhi wa sallam) said, "Say: My Rubb is Allah and then remain steadfast.'' Then I said: "O Messenger of Allah! What do you fear most about me?'' He took hold of his own tongue and said: "This.''
[At-Tirmidhi]

'Uqbah bin `Amir (radiallahu anh) said: I asked the Messenger of Allah (salallahu 'alayhi wa sallam), "How can salvation be achieved?'' He replied, "Control your tongue, keep to your house, and weep over your sins.''
[At-Tirmidhi]

In another Hadith, disadvantages can also be caused by the improper use of the tongue

Abu Hurairah (radiallahu anh) reported: I heard the Prophet (salallahu 'alayhi wa sallam) saying, "A person utters a word thoughtlessly (i.e., without thinking about its being good or not) and, as a result of this, he will fall down into the fire of Hell deeper than the distance between the east and the west.''
[Al-Bukhari and Muslim]

That is why, it is essential that one should think before he speaks.

Abu Hurairah (radiallahu anh) reported: The Prophet (salallahu 'alayhi wa sallam) said, "A man utters a word pleasing to Allah without considering it of any significance for which Allah exalts his ranks (in Jannah); another one speaks a word displeasing to Allah without considering it of any importance, and for this reason he will sink down into Hell.''
[Al-Bukhari]

Abu 'Abdur-Rahman Bilal bin Al-Harith Al-Muzani (radiallahu anh) reported: The Messenger of Allah (salallahu 'alayhi wa sallam) said, "A man speaks a good word without knowing its worth, Allah records for him His Good Pleasure till the day he will meet Him; and a man utters an evil word without realizing its importance, Allah records for him His displeasure till the day he will meet Him.''
[Imam Malik and At-Tirmidhi]

This Hadith tells us a fact which can be observed in our everyday life. Sometimes a person utters a good sentence which pleases an individual and he reforms himself or holds himself from doing something wrong. Such a sentence or utterance is highly rewarded by Allah. Similarly, sometime a person utters a mischievous sentence, the ruinous effects of which he does not realize. This utterance hurts someone's feelings and leads him to sin and evil. Almighty Allah is displeased with such a person. The lesson that this Hadith has for us is that one should strictly guard his speech and weigh his words to avoid Allah's Wrath.

Therefore, all of us should worry about words and take care in what we say, because Allah knows everything that we said as mentioned in Quran "Not a word does he (or she) utter, but there is a watcher by him ready (to record it)." (Quran 50:18)

Here are some advice for avoiding sins of the tongue:

1. Stay out of conversations that do not concern you.
2. Avoid arguing, even if you are in the right.
3. Do not say anything about someone else unless it is true, good, and useful. Say something bad about someone only if it is truly necessary to avoid a greater harm, such as to protect someone from becoming a victim of a crime.
4. Think before you speak; like feathers from a pillow blown away by the wind, words cannot be taken back, and their effects cannot be undone. You cannot control how others will respond to your careless words or what their effects will be. All you can do is control what comes out of your mouth to begin with.
5. Do not use language to try to impress people or sound cool. Use normal, proper speech and avoid slang, excessive eloquence, and false accents.
6. Do not swear or use obscene language. One narration from the Holy Prophet (peace be upon him and his progeny) states, “Heaven is forbidden to whoever is used to swearing/cussing. He cannot enter it.” It also destroys your respect in the eyes of others.
7. Speak the truth, even if it is against you. Let your word be reliable.
8. Avoid sexualized speech or dirty talk. Do not degrade the opposite sex or your own through your words, ever, and do not cheapen marital relations with your tongue.
9. Do not break confidences with your tongue. You should avoid saying anything to anyone that you would not want revealed to all, unless truly necessary. Likewise, you should never mention about someone else what they would wish to be kept private. For example, men and women should not talk about their quarrels or relations with their spouses to others, children should not carelessly reveal the bad habits of their parents, parents should not embarrass their children by talking about their past mistakes, etc.
10. Do not listen to any of the negative speech above, even in poetry or music – do not lend your ear to arguments, backbiting, bad-mouthing, cussing, obscenity, lies, etc., as even choosing to listen to such speech is sinful, it promotes such behavior from your own tongue, and it hardens your heart. Actively avoid such speech, and prevent or stop it when possible.

People who are careful about their words enjoy many benefits. Those known for gentle, kind, good speech and avoiding unnecessary and negative talk earn respect and trust from other people. Friends will feel safe with them, and people will be more at ease to do business with them. They will enjoy a good reputation. They hear more good things and thus learn more and are more likely to have an expansive and enlightened heart. There is no down side to guarding your tongue, and everyone can do it with practice and effort. No other part of the body commits more sins than the tongue, but if we are diligent, we can make ourselves the exceptions.

May Allah bless us with a tongue that is always engaged in mentioning Him, and help us avoid idle talk and uttering what is of no benefit in this worldly life and the Hereafter.

http://www.muftisays.com/forums/12-virtues/5069-guard-your-tongue.html
http://www.islamicinsights.com/religion/avoiding-sins-of-the-tongue.html
http://www.islamweb.net/en/article/152624/idle-talk