I have a standing order that pays £75 into a mini ISA every month.
this will cover my tax bill at the end of the year.
I have recently started paying myself £100 a week and the rest stays in my bank account for any outgoings.
Remember, everything you pay out for your business is tax deductable, so although you may take £200 in a week, you may pay out £70. You have your NI to pay and keep some back for tax.
If its your first year, you will probably get a tax rebate anyway, but do start squirreling money away just in case.
I strongly suggest that when you register to be self-employed, as someone to come out to talk to you its free. They will give you a quick reckoner to use, ie earn £100 a week, keep back XXX amount of money for tax.
I did my own tax return for 3 years, and this year have paid an accountant to file it for me. I filled every incoming and outgoing on excel sheets
on the computer and handed them in with all my receipts. I also work for a few colleges who PAYE, so also had to hand in P60's.
You are also allowed to earn nearly £5000 before you can taxed as well.