What should you do first in order to reconcile your checkbook register?

First, you need to have your bank statement and your check register.

Then, compare all your deposits from your checkbook register to your bank statement credits to determine the amount of deposit not yet credited by the bank, which is called your Deposit in Transit.

Next, compare all your disbursements from your checkbook register to all the debits in your bank statement to determine the amount of disbursements not yet debited by the bank.

Also, you need to check for any bank charges already debited to your bank account but not yet recorded.