Be prepared

You must get all your records together. Stephen Herring, an accotant at BDO Stoy Hayward, says: "All your income needs to be included, even if it has been taxed at source, so you will need details of such things as bank interest, dividend payments and state pension."

If you are an employee, you will need your P60 and, if you have received taxable expenses or benefits, your P11D. If you are claiming for expenses, such as subscriptions to professional bodies or part of your household bills if you work from home, get all this paperwork together.

If you are a higher-rate taxpayer you can also claim tax relief on charitable donations if you ticked the Gift Aid box.

Check the forms

Tax returns consist of several different parts, so you will also need to check that you have been sent all the right pages by completing page two of your tax return. If not, ring the self-assessment order line on 0845 9000404 for the relevant pages. If your tax affairs are deemed to be simple by the Revenue, you may have been sent the new short tax return.

Don’t get caught out

Ignorance of tax rules is no excuse for getting your tax return wrong. Sheena Hay, of Grant Thornton, the accountant, says: "One area that people commonly overlook is capital gains because they don’t know what to declare. "If you sell something and the proceeds exceed £32,800, this has to be declared even if there is no liability to capital gains tax." The capital gains tax pages also need to be completed to claim a capital loss.

Popular myths

The Institute of Chartered Accountants in England and Wales (ICAEW) points out that there are a number of tax myths that can get people into trouble when they are filling in their returns. These myths include the belief that money kept overseas is not taxable and that children’s income is not taxable.

People also believe that students do not have to pay tax in their first year at university and that if you let a room to a lodger the income is not taxable. If you let a room, up to £4,250 is exempt. Other myths include the belief that the state pension is not taxable and that you do not need to pay tax if you work for cash.

Do not assume that if you have overpaid tax you can always rely on the Revenue to pay it back. If you are doubtful about what you should be including on your tax return, or are not sure how to claim back overpaid tax, ring the self-assessment helpline on 0845 9000444.

Common mistakes

If you do not fill in your return correctly, it will be returned to you and you could miss the deadline. The Revenue lists five common reasons for tax returns being rejected, one of which is failure to submit supplementary pages of the return. Failure to complete the self-employed pages is another.

The remaining three reasons are: detailing information on separate schedules instead of on the actual return; putting notes, such as "per accounts" and "information to follow", on the return instead of actual figures; and failure to sign and date the return.

Keep copies

Once you have completed your tax return, keep a copy of the completed form and a copy of all the information on which you have based your replies. When the time comes to fill in next year’s return, being able to refer to what you submitted this year will be a useful starting point.

What happens next

You may not get an immediate reply from the taxman, but you will be informed of how much tax you owe before the January 31 deadline for paying your tax bill. Don’t despair if you miss the September deadline, file your tax return over the internet instead.

If you need help completing your tax return, contact your local tax office or the self-assessment helpline, which is also open evenings until 8pm and on Saturdays from 8am to 4pm. There are also useful guidelines on the Revenue website at www.hmrc.gov.uk.

To find a chartered accountant to help you with your tax return, contact the ICAEW on 020-7920 8100 or look on the internet at www.icaew.co.uk.