I've been stalking these forums for months when it came to all the different info I needed with visas. However, because the Tier 1 is so hard to get and there are only a small amount given out every year there wasn't that much information online about it. Fret no more! Today I'm going to go through what I did to get my approval from Tech City for stage 1 (info on stage 2 coming soon).
1. I have no PhD or published books. I have an MSc in Actuarial Science from a London University (I came here on Tier 4 and moved to Tier 2 and then soon Tier 1). I have worked legally in the UK for 3 years building up a career in digital marketing and user acquisition for mobile apps. It's a niche field, but it's quite in-demand especially at London-based startups.
2. Before doing any legwork, I emailed the TechCity people and quickly pitched them my experience and asked if they were likely to approve. I got a reply within 1 day saying they definitely need people with my experience and if all evidence is provided then they will most likely endorse me.
3. I got together a recommendation letter from my current CEO and a recommendation letter from the CEO of my previous job to cover that criteria. Then I got a letter from a cofounder to explain how I show exceptional talent in my field (though for the most part I was going for exceptional promise and/or talent). My CV and all the filled out forms were quickly finished too. The one thing I was concerned about was the covering letter. How'd I do that?
4. For my covering letter I reached out to a London-based solicitor who specialises in visas and they helped me make mine perfect for the Tier 1. The template I shall share with you below to better your chances.

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To,
UK Visa & Immigration Home Office
Tier 1
PO Box 496 Durham
DH99 1WQ
## Month ####
Dear Sir/Madam,
I, xxxxxx, DOB: ##/##/####, [country] national, hereby write this letter in support of my application for my Tier 1 Exceptional Talent Visa in my field of [Field]. I satisfy the relevant criteria for the grant of my application as follows:
Why you want to base yourself in the United Kingdom?
[paragraph] <- Be honest. I put personal and professional reasons in here.
What your occupation will be in the United Kingdom?
My position in the United Kingdom will be [position].
Which region or city of the United Kingdom are you planning to live in?
I plan on living in [area].
How do you demonstrate continuous learning?
[paragraph] <- Really go to town with this paragraph. This is the meat of the letter. Go through each role on your CV that led you to your current skill set and date each role to show a clear progression of learning.
How will the UK digital technology sector benefit from your work? (examples of this
might include the technological advances you will bring, the creation of new markets,
the planned growth of a company, the activities you will take part in outside of your
direct occupation)
[paragraph] <- I put my biggest accomplishment to date in this paragraph and my hope to continue bringing this high value to British startups.
What are your long-term plans in the UK? (through this visa route you can be granted
5 years of leave, which means you are eligible for indefinite leave to remain. Would
you consider staying, or would you like to move somewhere else after 5 years)
[paragraph] <- In this I detailed how I very much wish to stay in the UK for the long-term.
I herewith enclose the following documents in support of my application and duly meet the criteria for the grant of my application:
[table] I put a table showing each form and letter I had enclosed and what criteria it met.
I trust you will find everything in order, and I remain at your disposal for any further information that you may need. Thank you very much for your time. I hope and look forward to a favourable response to my application.
Sincerely yours,
[signature]
xxxxxxx
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5. After getting the cover letter finished, I shipped this off. I ticked for the fast track option for "growth" so I was hoping to have a decision within 18 days. 1 day after mailing my application I got charged on my credit card so I knew they had already taken in the application. 18 days after I sent in the application was a Saturday, but I got an email announcing my approval on the Monday after. It took roughly 20 days from sending the application to get approval.
6. Now onto stage 2. I'm going on holiday for the next month, so I cannot immediately apply for stage 2, but once I get back I will be submitting my application for stage 2 and will update you on that progress. I hope this helped!

Evan