If you are trying to get below £100,000 or simply save more efficiently, the two main routes are salary sacrifice through your employer and a personal pension or SIPP.
Salary sacrifice
You give up gross salary and your employer pays it into your pension. Because the money never becomes your pay, you save income tax and employee National Insurance, and your employer may share their NI saving too. It reduces your ANI directly. The catch is that you need your employer to offer it, and it can affect figures based on salary such as mortgage affordability.
SIPP (relief at source)
You contribute from net pay, the provider adds 20% basic-rate relief, and you claim higher-rate relief through self assessment. The gross contribution reduces your ANI. You get full control over where the money is invested, but you do not save National Insurance.