I have known very few people during my life who speak the truth lovingly, and practice wisdom and discernment with their words.  Especially when it comes to difficult conversations.  Most of what I've seen has been delegating the job, not communicating at all, or communicating in a manner that results in unnecessary wounds.  
The people I've spent time around who communicate truth lovingly have something in common; they have nurtured relationships with Jesus. 
Ephesians 4:15 ~ ". . . speaking the truth in love, we will grow to become in every respect the mature body of him who is the head, that is, Christ."[1] 
  kindnessCredit: Jennifer SweetOnVeg.com
Relationships are a blessing, and the times I've been corrected by leaders (or held accountable by friends) with hearts for the Lord, have been hard but not offensive. People have been pointed with their messages, but also loving and supportive.   
A key factor to keep in mind when preparing for a potientially challenging conversation is prayer directed to the Lord.  He makes it clear to seek Him for wisdom -- James 1:5.[2]  His meticulous knowledge of the hearts and needs of each of His creation makes Him the ultimate source of wisdom.
I spent years speaking facts to people without bathing potential conversations in prayer.  Then one day I was  in a prayer group and one of the ladies prayed regarding a need of one of her children.  The prayer caught me off guard and gave me something very new to think about. She prayed that anyone who wanted to approach her children about something would be prayerful about what to say, when to say it, and whether it should be spoken at all.  When I heard her praying, I remember thinking, "We're suppose to pray about things like that?"  
Since then, the more I've thought about it, the more I've realized some things.  More people experience more offenses by well meaning friends, family or whomever. Even in the most innocent of conversations, things are said without any mal intent, that are either ill received or poorly and carelessly delivered.  I'll reiterate that often there is no mal intent what-so-ever.  And even in the most innocent of conversations everything is ok, until it isn't.  My pastor has chosen to speak entire sermons on the topic of offenses and I've spoken with too many people who have expressed unresolved offenses in their history.  
Reflecting on these situations brings this passage to mind:
For you created my inmost being; you knit me together in my mother's womb. Ps. 139:13[3]
It might seem like an unexpected passage to refer to, but stick with me for a moment.  If you were expecting to engage in a potentially difficult conversation with someone (regardless of how well acquainted you might be with them) wouldn't you want to have an idea of the best possible approach according to who they are and what they need?  A respectful, truthful and most importantly loving approach.  
Who better to open our eyes to an appropriate approach than our creator.  He knows every person at the deepest possible level including their needs.  Based on His perfect knowledge, He can show us when to speak and He can speak through us, to the point that when it's all said and done, we know we weren't the source of the message.  He can even give us a loving tone.  He can also place it on our hearts to wait prayerfully before speaking at all.  
Here's another perspective:  As we pray and solicit prayer from trusted people in our lives, He can prepare the hearts of all involved.  Does this mean everyone is guaranteed to be full of radiance and joy after the conversation?  Well. . . no.  It also doesn't guarantee the conversation will be easy.  What the Lord promises is peace that surpasses understanding as we pray and offer Him praise and thanks.   
Ask Him for it and thank Him for it.