Hi
If you HAD BEEN on accrual basis in 2011 then you would have accrued that income, let's say $20K in 2011.
Example (2011 entry under accrual)
DR Receivable for services $20,000
CR Services Income ($20,000)
Then in 2012 when you received the check you post this
DR Cash $20,000
CR Receivable for services ($20,000)
But in 2011 you were not using accrual so - in 2012 at receipt of check if you had no accrual you post this:
DR Cash $20,000
CR Services Income $20,000
and from now on when you earn services income you need to record it by accruing it. OK?