The simplest way is to keep a folder with all the invoices/till receipts for items you ve bought and another one for the invoices you ve raised for your customers. In addition, use Excel to keep track of what s coming in and going out so that you can see how you re doing weekly/monthly/yearly.Even if you trade enough to be VAT registered (or you opt for voluntary regulation) you can still use your Excel spreadsheet to do your VAT calculations for your return. (I ve done this for years)Good luck with your new business!
separate folders for bills (goods purchased), separate ring pull folders for different monthly/quarterly bills, such as bank telephone, credit card, etc, keep a profit and loss account on excel, it makes life easy for you, accountants like it as well.
I would suggest using Microsoft Access but also print off copies just in case you lose the ones on the computer. Use separate folders for the printed copies
Word Excel