Notify past employers, unemployment and loan companies of any address and mailing changes. One forgotten W2 after you file your original return means amendment fees and tax liability. Generally I see this range from $49 to $350. When you amend Federal you need to amend state, which can also add more charges!
Sometimes in our hurry to get taxes done and out of the way we forget about the 6 weeks of unemployment in January for construction or a temporary holiday job that paid out wages in January for hours worked in December.