I keep a ledger which itemises every job I do, and what I am paid for each job. I fill it in when I get home each day. It only takes a few minutes.
I also itemise every expense, and keep all supporting receipts.
At year end, the totals go on my tax return and are submitted. Job done, and if the Revenues Commission (Irish Inland Revenue) want to spot check me, my books are ready and waiting.
John