Obviously, this is more appropriate in some cases than others- a minor disagreement might be put to rights with a phone call, and other times an in-person apology is best. But if you are apologizing for a mistake in a business capacity; or if in your personal life there is a long-standing issue to resolve; or you have hurt someone emotionally- a letter may add more weight to convey your sincerity.
As with any apology, the sooner it is shared, the better. That said, don't dash off an apology unthinkingly. Take your time to write thoughtfully, choose your words carefully, and consider the relationship between you and who you are writing to when setting the tone.
For an apology to a group of people, or an apology related to your professional work, type the letter and use a business letter format. Be concise and start right off with saying you are apologizing and what for. Explain, as far as you can, what went wrong. Share what you will specifically be doing to rectify the situation. If you are writing about a debt you are late in repaying be especially brief, and share the timeline it will take for you to repay that debt.
When apologizing to someone with whom you have a personal relationship with, consider handwriting your letter. It adds a more personal touch that will better convey the effort and thought you put into the apology . Start your letter off by stating what the situation is; you don't need to go into a ton of detail as the person you writing to is part of the situation and knows. However, by establishing what has happened, you are setting up the context for your apology. When you apologize say what for specifically. If you don't; it sounds a bit insincere, as if you don't know what you did wrong, and if you don't know what you did wrong there is no reason for the other person(s) to think you won't do those same hurtful actions again. If you feel that both you and the other party or parties are to blame, this is not the time to emphasize that point. Say you would like to take responsibility for your own part in this situation without mentioning the other person's or people's role(s). Now is the time to focus on your actions and not others' actions; focusing on others makes it sound like there were mitigating circumstances and you acted as you did for reasons beyond your control. If you are apologizing, you must take ownership of those actions, even if there was no intent to hurt the other party.
In most cases, after you have apologized, you should also offer up what you will do to change that situation. How will you act in the future ("I will try to be more considerate of your feelings," "I will make and effort to call if I will be late")? You may also want to ask whether there is something you can do to help repair the damage that has been done. It is a good idea to also state a specific action you will do- maybe ask to meet for coffee so you can apologize in person, for example- and follow through on it. Even if you have asked them for ideas on what you can do, people may be reluctant to take you up on the offer and your relationship may not get rebuilt; if the other party sees you following through on that specified action, they are more likely to realize you are serious in your commitment to repair a damaged relationship.
Depending on the situation, you may also want to send a gift along with the apology letter. This is can be very effective in helping ton show your feelings, but you do walk a fine line with gift giving, for several reasons. First, always take into consideration your past and current relationship with the other party or parties. Don't send a stuffed bear to your ex; you don't have that level of intimacy any more. You also want to be careful that your gift does not make it look as if you are trying to buy someone's forgiveness or love. However, a bouquet of flowers along with an apology to your friend after you stood her up for lunch is a way to communicate she is a valued person to you. Your own judgement and discretion should guide you in this area.
Have you ever had to write an apology letter? What were the results. Please feel free to share below as encouragement and advice for any who may be struggling to write one right now.