The Charity Commission for Northern Ireland has made available extensive guidance, here. This includes, R&P and Accruals guidance, and how to complete the reporting forms.
The Charity Commission for England and Wales has produced a number of detailed guidance publications, including the key SORP documents and CC32 which you can find here.
The OSCR offer a receipts and Payments Accounts Work Pack: Guidance booklet and have updated their advice on improving charity accounts.