Helsi, what are you going to try and do? Becoming self-employed is a doddle, I recommend you get yourself a good accountant. Some specialise in small businesses/subcontractors/sole traders. Mine only charges me around £200/year and is worth his weight in gold.
Decide whether you are going to be a sole trader or a limited company. There are tax advantages in being a limited company but the paperwork is more and the accountant's fees more. I have been self-employed as a sole trader for 8 years and have quite a simple business - I send out a few invoices a month and I don't buy much in in terms of subcontracting work, and have found being a sole trader suits me fine.
If you plan to turn over more than a certain figure (around £60K I think but don't quote me) you'll need to register for VAT. But you don't need to do this until you actually hit that figure. If you have to buy in a lot of VAT-able items it might be worth registering anyway as you can claim back the VAT you pay on them.
Make sure you keep all your receipts for petrol and stuff even if it's not directly related to your business. Your accountant can decide how much you'll be able to get away with claiming for.
If you're going to be doing anything that involves working with members of the public make sure you have sufficient public liability insurance. Many 'office at home' insurance policies include this in the cost (I pay £12 a month for mine and don't come into contact with the public, but still have millions of £s worth of cover)
As for earning a living: make sure you invoice promptly, that your customers know exactly when they have to pay you by and that they can be liable for interest and compensation if they exceed that date (see here for details.)... and chase them if they don't pay! Some big multinationals 'earn' millions a year by delaying payments to their creditors.
oh god yes: the bigger the company, the harder it is to get them to pay up. In 10 years of trading (mostly dh as a sole trader, lately the two of us as a ltd company), we have had one invoice that we had to cancel because they didn't pay and it became more aggro than it was worth to chase it up. That invoice was to....BT
thanks to you all. It's actually for dh. He is an experienced head chef and wants to go s/e as a relief chef covering at various places during times of sickness, holidays, when extra cover needed etc. not many jobs about to his level at the moment. need to do something and fast as we need the money and also he's geting depressed.