If you just opened a business or you intend to open one it is important to have control of your papers.
The invoices issued and the receipts for service of goods purchased should all be kept because these are the things which will determine your income tax.
If you are an organized person probably you will have an Excel spreadsheet to record all of these papers. The people whom are not so well organized probably have a bag/box full of receipts.
What do you have to do in order to avoid at the end of the fiscal year the surprize of having to pay an unexpected high income tax?
Create an Excel spreadsheet or use a bookkeeping software and introduce all of your receipts or invoices every day or once a week.
If you are not this type of person than go with your bag/box of papers to an accountant on a regular basis, which could be monthly or quarterly. You will pay probably 1-3 hours for bookkeping serivices and you will know your financial situation and most probably be on time with your filing tax return, this way avoiding penalties.
Another benefit but not the less important is that you will know what to expect regarding your tax numbers.
Have a succesful business!