If you are doing your self assessment for first time, make sure to avoid mistakes that could result in penalties for paying wrong amount of tax. Please consider the following few things in mind before filing it:
UTR reference number
You need to quote your unique tax reference (UTR) on your tax return. This is 10 digit long and you’ll find it on HMRC correspondence such as a Notice to Complete a Tax Return. Put in your UTR when asked for your tax reference number.