The best thing you can do is get a good accountant to guide you through this. A Revenue audit can be very time consuming, costly and stressful.
If you're not prepared to do that then familiarise yourself with the Revenue audit code available on the Revenue website. It sets out what Revenue can and can't do or ask.
You need to look at the scope of the audit, what taxes are covered and what years. Sometimes Revenue issue an audit notice for "all taxes and duties". If you get one of these then you should be prepared for the auditor to look at absolutely everything, even things you might never think of such as mortgage interest relief.
If it is for a specific tax, eg income tax, you should start with the returns for the years to be audited and have supporting documentation for every figure in returns. You should have profit and loss accounts for each trade and rental accounts for the rental income. You should have supporting documents for each transaction in those accounts.
You'll also need all bank statements, cheque books and lodgement books for the years to be audited - business accounts and personal accounts. You may even need credit card statements.
You mention artists exemption. They'll probably look at your entitlement to that and whether the income you claim under actually relates to it.
You should also look at what tax credits you have claimed and make sure you were entitled to them.
If you think you may have an issue you can make a disclosure and avail of reduced penalties.
It's sometimes useful to give the auditor a call when you receive the notice. I always ask what has triggered the audit. They don't have to tell you, and often don't, but if you explain that if you know what has triggered it then it may help in the preparation they sometimes give some indication.
But, as I said initially, the best thing to do is get a good accountant or tax advisor. It could save you a lot of time, trouble and expense in the long run.