What is the first step toward reconciling your checkbook register?

The first step is to gather the documentation needed to complete the reconciliation: the check register, the bank statement and the previous reconciliation.

While you can complete the following steps in any sequence, I think it makes sense to first compare the reconciling items from the previous statement to make sure they are no longer reconciling items: have all outstanding checks been presented, have any deposits in transit been credited, bank fees recorded, etc.

Then you would compare all checks recorded in the register to those which have cleared the bank, noting any discrepancies.

Then do the same for deposits.

Finally, identify any charges or credits on the bank statement which were not posted to the check register.

As long as you complete the reconciliation, it really doesn't matter which step you do first. I believe the above sequence makes the process easier.