You can do your own Self Assesment on line every year, You will need a printer etc. When you register S/employed hmrc will give you a uniqe refference number. keep it safe. Use it to log into HMRC.
You will need a self assesment Template,
Dates worked,
hours,
money taken,
money spent,
fuel etc, mots etc Bussines expenses, phones equipment, much more.
add all takings up, Deduct expenses etc. Total left. Something like this
eVERY YEAR FILL THESE DETAILS IN AT HOME ON sEPERATE MONTHLY ACCOUNT SHEETS, dO THE SAME ONLINE WHEN YOU FILL YOUR YEARLY SELF ASSSMENT