"...but no human being can tame the tongue. It is a restless evil, full of deadly poison. With it we bless our Lord and Father, and with it we curse people who are made in the likeness of God. From the same mouth come blessing and cursing. My brothers, these things ought not to be so." ~ James 3:8-10 ESV
I almost always find myself thinking James's emphasis would be better served if an exclamation point were placed at the end of the last sentence in the passage above. The things James speaks of in the third chapter of his letter strike close to home for me, because the way I speak and communicate have been some of the focus points that the Lord has continually pointed out to me with greater and greater emphasis in the last few years.
The passage that has most impacted my view on this subject is Ephesians 4, and within that chapter verse 29 has been embedded upon my heart - though, admittedly, not to the extent that I pray it one day will:
"Let no corrupting talk come out of your mouths, but only such as is good for building up, as fits the occasion, that it may give grace to those who hear." ~ Ephesians 4:29 ESV
The NASB words it like this:
"Let no unwholesome word proceed from your mouth, but only such a word as is good for edification according to the need of the moment, so that it will give grace to those who hear."
Of course, whenever it comes to correcting your tone of voice toward a sibling/child who is (in your mind) making a nuisance of themselves, or the way you communicate an idea/conviction to a friend, your emotional state and thoughts need to be dealt with as the 'heart' of the matter.
"...For out of the abundance of the heart the mouth speaks." ~ Matthew 12:34(last half)
(See also Matthew 12:33-37, 15:10-20, Luke 6:45... also the Psalms and the book of Proverbs are full of references to different aspects of this concept)
But there is still the clear fact that we are commanded (by God's grace in the sanctification process) to constantly seek to better control our words, that we may only ever speak in a way that honors and glorifies our LORD.
May we ever persevere to keep any kind of 'cursing' (i.e. actual curses, cussing/profanity, harsh words, slandering, gossiping, 'giving a hard time,' crass or lewd conversation, etc...) from our lips. And may we not only stop these things, but start proclaiming - by word and deed - the name of our precious Savior, Jesus Christ, and his gospel to everyone we meet.
"Preach the word; be ready in season and out of season; reprove, rebuke, and exhort, with complete patience and teaching." ~ 2 Timothy 4:2 ESV
"Finally, brethren, whatever is true, whatever is honorable, whatever is right, whatever is pure, whatever is lovely, whatever is of good repute, if there is any excellence and if anything worthy of praise, dwell on these things." ~ Philippians 4:8 NASB