for my two penneth worth, i would give the following advice that i've learnt the hard way! Its not just about painting its about marketing yourself and running the business side of things too. ANy fool can get out of bed and work for nothing so heres the things i would suggest you consider:-
stick to what you are good at and what you want to do. have a clear plan.
don't be frightened by a job. break it down into small tasks and get a clear plan in your head. don't bite off more than you can chew though. Its better to do smaller jobs and build your confidence and keep the cash flow going when you start, rather than a big one where you may feel overawed and could take a knock on the price.
Be professional. Learn a script to tell customers when you talk to them for the quotes. eg offer references, only use decent materials, only do one job at a time. Sell yourself but don't make promises you cant keep. Have a portfolio you can take with you. business cards are good and be professional.
Always do a written quote and get them to sign it no matter how small a job. Get a decent accountant who can tell you weather to go as a sole trader or limited company and who will tell you what to do and what records to keep. They WILL save you money.
Watch your turnover. its very easy to go over the vat threshold without realising it. Also consider where your main work will be. If you do a lot of commercial work then you will appeal to commercial clients more if you are vat registered.
be punctual, be tidy, clean up as you go and at the end of each day. Be organised, have the materials you need already. Time you waste rushing around to get a pot of paint you forgot is wasted earning time.
get to know a couple of decent trade suppliers. explain you are new to the game. they know you will put business your way and they want your loyalty. they will help you. There is no point rushing from b&q across to wickes and back to homebase to save £2.00 on some paint. Get to know your materials. Decent materials don't cost much more and save you time.
Your time is precious. Dont waste it. Buy decent tools that will do the job and make life easier. The same with materials.
Dont over advertise. Everybody wants your advertising money. Most of them are a waste of time. One of our best advertising returns comes from the friday ad. you cant beat recommendations though, they are free and they give you a foot in the door.
If you have a van/car etc get it sign written or get some magnetic signs. Its a moving advert board and people will also see it parked outside jobs. Customers like to see a name when you turn up for quotes. It looks like you are there to do business not a fly by night in a battered plain white van.
keep records of everything. Dont **** off the taxman or the vat man. Its a personal choice but these days it is a big risk to do "cash in hand" and if you get found out it is painful!
Talk to your bank and get a business account. Internet banking saves money. they will give you free banking and advice and help. also useful for any trade accounts you want to open. ALWAYS put the money for the tax man into a savings account and DONT touch it. Open a savings account and put some buy for rainy days.
keep your customers informed as the work progresses. they like to know the game plan and whats being done next etc. get to know any after care they need to know, eg can they wipe down the paint etc. its reassuring and shows professionalism.
If theres a problem and its down you, go back and sort it. customers accept little problems occur and are grateful if you put it right. what they don't like is people that don't come back.
you will soon gain contacts eg another painter who can help on bigger jobs, electricians etc. Dont recommend people who you aren't sure of. customers don't like running around trying to find umpteen different people to do jobs. if you know a plasterer who can do a decent skim and you can put work his way and vice versa it can work well. it also means you get to know each others work and make life easy for each other.
consider public liability insurance. what happens if you spill that paint over the carpet?
Dont be scared to lose a job on a price. Theres no point doing a job for nothing. while you are doing that job you could be earning on another. Work out a reasonable day/hourly rate. with experience you will get to know how long a job will take etc. price up the materials then price up your time. work will come in. be patient as well. people will get quotes from several people and they may not come back to you for a month or two.
Have some basic terms and conditions to put on the quotes, eg payment terms, all rooms to be clear of furniture, normal hours of working etc.
There are many people out there who will help when they know you are a new business. have a look at
www.startups.co.uk
Be under no illusion working for yourself is hard work. it takes over your life because you no longer get up in the morning and go to the office, come home and pick up the pay cheque at the end of the month. You go to work, answer the phone while you are there, make appointments, organise other jobs, come home, go out to do quotes, come home, write out qoutes, do a bit of book keeping etc etc. It gets easier as you get systems in place and you gain experience.
experience will come thick and fast and you will be on steep learning curve. Confidence will take longer to come however. don't worry when things go wrong and it takes a knock.
There is no better feeling when you finish a job, the customer is happy and you get a cheque there and then. you've generated that money and boy does it feel nice.
one last thing. the advice my father always gave me. Buy a decent broom and learn how to use it. If a job looks neat and tidy when the customer comes home, they will be happy!
Good luck, i wouldn't change working for myself for the world.