First of all, the answer by Sourav Ghosh is entirely correct, however speaking as a hiring manager there are a couple of points I would like to add. 1, 2 and 3 are specifically related to how you write your CV, 4, 5 and 6 are more generally around how you apply:
- Write your own submission
In addition to the point about customising your CV and cover letter to each role, I want to say: do not, under any circumstances where you actually want the job, use the automatic apply button on job websites. When I have a job opening I see hundreds of these automatically generated applications from the likes of Indeed.com, they are almost entirely terrible and frankly I don't have time to dig through each one, find the website profile and attempt to judge if this person is worth my time. I know it takes you a bit longer, but please, please, please write your submission yourself! It shows me you care about your application and haven't just hit "apply" on a hundred job adverts without reading them.
- Do include any relevant training courses
While your school based education may have finished with A-levels, any relevant training you have done is worth including (even free online courses from LinkedIn or W3Schools or similar count if you have nothing better). Demonstrating that you are committed to personal and professional development will definitely get you further up the list.
- Make your submission stand out
Make me notice your CV. I know not everyone is a graphic designer but make your CV catch my eye. Something nicely formatted with considered use of colour is perfect. Google for "modern CV template" for ideas. However make sure the colour and design don't overtake your content, that is what I'm really looking for.
- Don't bother including a photo
I'm hiring developers, not actors to star in my latest West End musical, I don't care what you look like. In fact, with modern "blind" recruitment practices you may find it gets filtered before it even gets to a hiring manager, along with names and anything which may induce unintentional bias.
- Research the company, if you can
While not always possible if going through a recruitment agent, if you know the company you are applying to, show me in your cover letter that you have at least a vague idea about what we do. Tell me why you're exited to work here (even if you're not) and what made you want to apply (beyond "I need the money"). Speaking of recruitment agents...
- Avoid recruitment agencies wherever possible
Honestly, recruitment agents are the absolute bane of my existence. They pester me constantly even if I don't have roles advertised, their salary expectations for the people they send are wildly unrealistic and frequently they have no idea about what I as an employer actually need from my people. I often question if even they read the job advert. If you can apply directly, I strongly advise you do so.