6 months cash fund, for emergencies
Then, depending on personal circumstances; pension, ISAs, other investments,
Pension
I assume you are in your mid 30s, so pensions aren't the top priority, but its very tax efficient.
ISAs
Being in your mid 30s you can put £4k in to a LISA, get a £1k top up from the government, and then the balance of your annual ISA allowance in to a stocks and shares ISA - something low cost, passive, tracker. Lots of options out there, Vanguard/HSBC/Blackrock/Fidelity. Each has its own quirks, but pick one and invest in a global low cost tracker and then let it grow. Long term, i.e. more than 10 years, its the best place for your money.
Investments
If you are happy to lose a big chunk of your money, then BItcoin or another crypto currency is something to consider. Personally, i avoid them, as I don't understand them, and I prefer to invest in things I understand.
Other things to consider are personal circumstances; married, kids, partner, wills, attitude to risk, etc..