Writing a business plan should help guide you. It’s also needed for presenting to the bank etc. Your business plan should include a mission statement, a company summary, any service or product offerings, a description of a target market, financial projections and the potential costs of the operation.
Identify your market - do your homework. Assess the market, targeting the customers most likely to buy from you. Work out a realistic assessment of costs/charges etc.
A good accountant helps enormously - go visit a few - interview THEM - ask them how they can help you etc.
Communication - so many small businesses fail because the proprietors, while good at their job(s) are often crap at getting back to people. Folk hate being ignored. Answer that phone/email right away.
Patience - keep in mind that success won’t necessarily happen overnight. It could take some time before you make a profit.
Promotion - plug, plug, plug away, Facebook, Twitter etc. Use any/all 'free' resources you can to promote the business. Nothing beats some good old-fashioned word-of-mouth marketing. Get friends, family members etc. to spread the word about your product(s) or service(s.)
Don’t 'bad-mouth' the competition when talking to customers. If competition exists, it means there’s a market for your business. Use this to outperform a rival - offer a 'better' service - but don't get into 'slagging off'.
Make sure folk pay on time. Many businesses fail because of cashflow (or lack of) - it's no good being owed loads but the phone is about to be cut off. Set out terms sight away and make sure you deliver on time and the customer pays on time.
Say goodbye to your social life for a while.
You think you'll be working for YOURSELF - you won't, you'll be working for your customers.