Have you ever thought how much you want to say, give information to someone but you can’t say it out loud? We often forget what we wanted to say. When you write your thoughts, you won't forget them.
You need just a pen and a piece of paper. Instant start writing what you think, what you want to share with someone. Don’t be afraid to express feelings on the paper. Letter is a great means to the agreement, because others can read it many times and empathize with the emotions which you wrote. Often happens that when we try to talk with someone, when we want to solve some problem, conversation turns into an argument. Advantage of letter is possibility to express your opinion, anyone won't interrupt you, and recipient will read it as a whole.
In the letter you can write what irritate you in someone or why do you like it. Don’t focus only on the flaws. You can express what in particular make you tired, what would you like to change. Be the person which cares about relations. People to whose you write the letter may be parents, siblings, partner or a friend. Best if you deliver the letter personally, but this is not necessary. Effects can pleasantly surprise you. Words on the paper have plenty of power!