After decades of paying into Social Security, you're finally ready to get some money back out of the program. All that's left to do is navigate the sign-up process. It sounds pretty simple in theory, but if you want it to go as smoothly as possible, you need to do the following three things in advance. Feel free to start them right now, even if you don't plan to sign up for Social Security for another few months.

1. Gather all the documents you need

The Social Security Administration already has some information about you on file, including the amount of money you've paid Social Security taxes on during your working years. But it still needs some personal information and documents from you to verify your identity and set up your direct deposit.

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You should have the following on hand when you apply:

• A certified copy of your birth certificate.
• Proof of U.S. citizenship or lawful alien status if you weren't born in the U.S.
• A copy of your W-2 or self-employed tax return from the previous year.
• A copy of your U.S. military service papers if you served before 1968.

If you're also applying for benefits on behalf of family members (i.e., minor or disabled children), you may need to provide documentation for them as well.

You'll also need to know your Social Security number and the routing and account numbers for the bank account where you want your Social Security checks deposited. These numbers should appear on the bottom of your checks for the account. Otherwise, you can ask your bank what they are.

2. Decide when to sign up

You probably know when you'd like to receive your Social Security checks, but you can actually apply up to four months in advance. Applying early isn't a bad idea because it'll help you avoid unexpected delays. For example, if you wait until you're ready to start claiming only to find out you're missing some key documents needed to process your application, you may not receive your first check on time.

You should also note that you're not going to see any money in your bank account as soon as you sign up. The government pays Social Security benefits in the month after the month they're due. So if you want March to be the first month you claim benefits, you'll get your first check in April.

Things can be even trickier for those applying at 62. Your first month of eligibility would be your birth month if you were born on the first or the second. But if you were born on any other day of the month, you aren't technically eligible until the month after your birth month. So a birthday of March 15 would mean you couldn't sign up until April, and you wouldn't receive your first check until May.

Make sure you have a plan for how you'll cover your expenses in the meantime. This could involve working longer or relying upon your personal savings. If you have any questions about when your first check will arrive, contact the Social Security Administration.

3. Know how much you can expect

Create a my Social Security account if you haven't already done so, and use the calculator there to estimate how much your monthly Social Security checks will be. The calculator shows how much you're eligible for at any age, so you can still get an accurate estimate even if you don't plan to sign up for a few months.

Make sure you understand the implications of signing up when you plan to versus claiming sooner or delaying benefits. The federal government assigns everyone a full retirement age (FRA) based on their birth year. It's anywhere from 66 to 67 for today's workers. If you sign up right at your FRA, you get the full benefit you've earned based on your work history.

Signing up early reduces your checks by up to 25% if your FRA is 66 or 30% if your FRA is 67. Each month that you delay grows your checks a little more until you reach your maximum benefit at 70. That's 124% of your full benefit per check if your FRA is 67 or 132% if your FRA is 66.

The right age for you to claim benefits depends on your life expectancy and financial situation. Those who expect to live into their 80s or beyond usually get a larger lifetime benefit by delaying Social Security, while those with shorter life expectancies may prefer to sign up early. You may also have to sign up early if you need Social Security to help cover your bills.

Only you can decide when you're ready to apply. If, after reviewing the above information, you decide you're not ready to claim yet, you can always put it off until later. Use your monthly benefit estimates to help you set a new target age, and then mark the date on your calendar so you know when you can sign up.