Since April 2017 the Scottish Parliament has been able to set income tax rates, with a starter rate of 19% with incremental charges as income levels increase. This rate is of course lower than the basic rate for UK taxpayers, but note the Scottish rates only apply to non-savings and non-dividend income.
You also have to be resident in Scotland of course, with the test determined by your usual place of residence. If qualifying, simply tick the appropriate box on the self-assessment tax return residence pages and the correct rates should apply. This wasn’t the case however for the 17/18 tax year when the wrong rates were applied if claiming the remittance basis but hopefully HMRC have sorted this wrinkle out for the new tax year.
The Scottish rates of tax ratchet up as income level rise, with the top rate of tax 46% which is of course higher that the UK top rate. We believe the cut off point is around £26,000 of earned income, where below this level you will be better off under the Scottish tax system; but before getting too excited, only by a maximum of £20 for the year. Above the cut-off point, you will be worse off.