Quoting from The Beginning of Guidance by Abu Hamid Al-Ghazali, as translated by Mashhad Al-Allaf (2010, pp.92-102):

As for the tongue, it was created for you only so that you could spend much time in the remembrance of Allah Most High and in recitation of His Book; that you could guide Allah’s creatures to His Way; and that you express your needs in worldly and religious matters. If you then use it for other than what it was created for, you have been ungrateful for Allah’s blessing. The tongue is the part of the body most able to overpower both you and other creatures. “People are not thrown into Hell on their faces for anything more than the harvests of their tongues” (Tirmidhi).

Struggle to gain victory over your tongue with all your might, lest it throw you onto your face in a pit of Hell. For it has been narrated in a hadith, “Verily, a man might utter a single word, and for this one word he is hurled to the depths of Hell a distance of seventy years” (Tirmidhi).

A martyr was killed in battle, and someone said fo him, “How lucky he is, he has earned Paradise.” The Prophet صلى الله عليه وسلم‎ said, “How do you know? It may be that he used to speak of that which did not concern him, or was miserly over things which were of no benefit to him anyway” (Shu’ab al-Iman).

The book details and lists the following 8 ‘calamities of the tongue’ to watch out for and avoid:

1. lying
2. breaking a promise
3. backbiting
4. disputation, argumentation, and competitive debate with people
5. ascribing goodness to oneself
6. cursing
7. supplication against creation
8. jesting, ridiculing, and making fun of people.

May Allah Subhanahu Wa Taala give us the ability to recognize where we go wrong and help us avoid such calamities. Ameen.