Actually there are important things to be said. When deciding to disfellowship often times elders look at how the person is doing spiritually as a direct correlation to their repentance. Do they feel like they have jahs spirit, do they earnestly pray for forgivness as well as in everyday life. Do they talk as if they have a personal relationship with him.
Now you just apply the same when trying to get reinstated. Tell the elders how you did not pray to Jehovah and did not feel worthy to be one of his sheep. Tell them how you had a bad attitude and was critical of others in the congregation causing you to stray. Tell them you didn't pray, never studied for meetings, never did personal study. tell them you thought meetings were boring and disliked field service. Now bring on the works that befit repentance.
Tell them When you were disfellowshipped you never felt more empty and alone. You cried and begged Jehovah for help. As you got back to reading the bible everyday, studying for all the meetings, personal study you very slowly and gradually felt Jehovah giving you his spirit. You developed a spiritual routine everyday. As time went on you found yourself talking and praying to jehovah all day long everyday. You couldn't wait to go to the meetings even though no one could speak with you, just being around his sheep became so refreshing to you. You read every watchtower and awake as soon as it is available. After awhile all you could think about doing was how you need to preach to others about your god. It was then that it hit you just how much you not only hurt those who loved you but how much you hurt jehovah. Reflecting on it all became very emotional for you once again. but this time you gave a very long and heartfelt prayer to jehovah. You actually felt his spirit encouraging you and uplifting you. It was then you finally knew you were determined to never let this happen again and never let your spiritual guard down. It was then you realized you were determined to return to hi and be in good standing whenever Jehovah felt the time was right.
And that about sums up your works that befit repentance. And probably wouldn't be a bad letter requesting reinstatement.