First of all a note: Freedom of information request also known as FOI is not the same as subject access request, also known as SAR
They are two completely different things.
The Freedom of Information Act covers any recorded information (data) that is held by a public authority in England, Wales and Northern Ireland, and UK-wide public authorities based in Scotland. It does not give you access to you personal data. An example of FOI will be meeting notes of a meeting or organisation structure of a department etc.
The right of access, or subject access request, also known as SAR is a right under GDPR law. Right of access permits you to request and receive a full breakdown of all the personal data you have shared with an organisation or the organisation holds on you. Think about medical data, school data, personal details etc.
The easiest way I have found to create a Freedom of information request is to do it online via website called www.whatdotheyknow.com
You start by making an account on the above website. Once your account is set up, click on new request and you’ll be prompted to select the public authority that holds that information. Once you select the public body (in our case it was Leeds City Council), you then write your Freedom of information request to them.
I will advise to search this website What Do They Know first to see if that information already exists in a previous FOI request made by some one else. This is also useful for looking at how others have requested information and can help you put together your request.