Make all the pension contributions that you wish to make by the April 5th deadline. This will be the lower of £40,000 and your earnings for the tax year, but subject to a lifetime allowance of £1,030,000. These rules are over-complicated if the Government actually wants people to save for a pension and not throw themselves upon the State in retirement.
Put up to £20,000 in an Individual Savings Account (ISA) by April 5th. Use it or lose it.
If you own a portfolio of shares, you might deliberately sell a few in order to crystallise a gain which is below the Annual Exemption of £11,700. There are rules to anticipate you buying them back the next day. Your accountant can advise you here.