You probably feel under pressure to write the perfect letter. You want to contact a long-lost relative and, for once, a letter feels the right way to do it. Nowadays, people have access to so many forms of communication, that letter writing is in danger of becoming a forgotten art. You can use your phone to call or text someone, or you can e-mail them. But the very instant nature of these forms of communication can make them unsuitable, in some circumstances. You know that writing this letter is going to be a challenge. You want to strike the right note, so you may need to be particularly sensitive. If you take your time and write the letter to the best of your ability, you will meet this challenge.
Plan your letter. Explore your purpose for the letter, as this is the key to how you plan and write it. You may be contacting a stranger who you have tracked down on a genealogy website. Alternatively, you may want to re-establish contact with a person who is estranged from the family. If this is the case, you may wish to discuss the letter with other members of the family before you write it.
State why you are writing the letter. Say something like: "I am making contact because I have discovered that we shared a grandmother". Keep your tone light and friendly. You need to make the person glad to get the letter, not feel as though you are intruding in an unwelcome way into her life.
Tell the recipient a little about your life and your family. If it is a person who is estranged from others in the family, tactfully offer an olive branch. Do not pressure the other person to respond in any particular way. Leave the door open for him to make contact. You may find it most appropriate to conclude the letter with your own contact details.
Show interest in the other person's life, without being intrusive.
Do not go into details of any dispute at this point.