Be aware of social media
Whatever you post whether it be on your Facebook page, whether it be on a forum, whether it be on an internet site or Twitter, that information is available to HMRC and HMRC will look at these sources for information to check your tax return.
One of your obligations is to ensure that your tax return is accurate and complete. HMRC is alerted to various entires in your tax return such as rounded amounts or what HRMC suspects are estimated amounts because HMRC will then believe that your record keeping is not being complete.
Use the "white box"
If there are any year on year inconsistencies or variances in your tax returns so for example if you have lived off non-taxable incomes one year or there's been a change in your business performance such as your gross profit rates for example a change of supplier then one could making entires in your additional information box, the white box as it's known, to explain this so that when HMRC risk assesses your return you will have made this situation aware to them.