The Small Charities Coalition has some great resources https://www.smallcharities.org.uk/resources-governance/
The Government has a step by step process you can see here
Ask yourself the key questions with help from CAF here
There are many types of fundraising, so you should pick the ones that are most relevant and achievable for you.
London Funders provide a comprehensive list of where you can find what funding is available https://londonfunders.org.uk/about/looking-funding/where-look-funding
If you want to apply for local funds the council has three opportunities which you can see here