A question regarding running a business

Not really sure how to answer your questions but I wish you the best of luck with this. ^-^

Only thing I could thing of would be to decide on a prices and perhaps post something somewhere about what you're doing and how much it is etc. Maybe even get your own basic website that shows price listings and perhaps examples of your work / what you're capable of doing.

Just start off small. Go on Craigslist or any local online websites that allows people to buy or sell stuff, then make a post saying that you can make websites for small businesses in your community. Make up an hourly or fixed rate. Ex: $10/h or $30/per page. Then wait for people to contact you. Also once you start getting bigger, then start printing out Business cards and hand them out.

Never ask questions about running a business, only ask question about running a successful business.
Rookie mistake.

I'm starting up a business too soon, and I know that it's a requirement here to have a business plan which outlines every aspect of the business (employees, duties, the goal of the company, what he offer, operations plan etc).

It's best first to learn everything you can about the tax system, so you don't fall into any trap holes if you start making a good amount of money, and yes, definitely make invoices with every service you provide as you will need them for tax purposes. Remember to also register your business name, and you should grab a domain and host your own website so people know you are a legitimate business.

A minimum wage job gets you ~£1000 a month..
UK VAT is 20%
.. earning anything under 10k a yr means you don't pay tax.

First off,

Best to see what your competition is.. See, if it is feasible to even go into business. Whether Website design or a Coffee shop.
Second, Find out what your Local Tax and Business Laws are. You can obtain these from your Local Government offices dealing in Copyrights.

Thirdly, Find a margin in which your services should cost. Don't undersell yourself.

Lastly, Sign me up as a business partner and give me 85%. Totally Legit.

As somebody that actually owns a small web design business I can tell you the following things.

1) Do not underestimate the need for signed documents. Everything should be well documented, on physical paper and make sure to get it signed by the client.

2) Be up front on costs, and bill your clients a rate that is fair for both you and them. You have little experience and this is an opportunity to build a portfolio and customer base. Treat it as such. Give your clients a steep discount compared to what they might pay a more established company, but at the same time don't deliver less product. It's very important that you be able to accurately give estimates on the time and cost involved in building a site.

3) You're a small business, as such you will likely be working with a similar client base. Most if not all of your potential clients are probably going to be brand new businesses or small local shops. Don't underestimate their lack of professionalism or business knowledge. There's a good chance you're going to wind up working with somebody just as new to the business world as you. Generally those people will grossly underestimate their ability to actually pay you, or at the very least on time. Additionally they will likely think they can get a full 30 page site with custom graphics for less than $100us.

4) This leads back to point 1. Document everything, especially finances. New and small businesses love to overestimate their ability to pay their bills. So make sure you lay out a payment schedule before you do even an hour of work. I require 50% deposit up front with a contracted date for the final payment. I do 50% up front and 50% 45 days later. If they can't expect to be able to pay you within a month and a half of you providing them a service they are not a customer you want to take on, trust me. This pays for the ability for me to sit at home and work while also being able to pay my bills on time. Without this I would not be able to dedicate 30-50 hours a week sitting in front of my computer working. This also protects you from getting scammed by "here today gone tomorrow" businesses and from people looking for services for free.

5) Finally, never work for free. Yeah you're new, but your time is worth something. As a young person you're especially vulnerable to adults trying to take advantage of you and get something for nothing. By documenting everything and contracting a payment schedule you protect yourself from getting scammed. Do this long enough and people will try to scam you. Everything from asking for a site design only to hire some punk kid for half the cost to rip the files from your test server, to simply pressuring you to put their site live even though they haven't paid yet and then never returning your phone calls again. You need to be wise to these scammers and protect yourself from unintentional charity work. As a freelance developer everything is on you. You succeed or fail based on the product you deliver and the business deals you make. Take everything you do seriously, but be aware that there are people out there who prey on young web developers exactly like you.