Before setting up your ledgers you should consult an accountant regarding how and what you are going to be keeping records of, the legitimate deductable items, and how to file your annual taxes.  Entries into your ledger should be made at the time of the transaction and should not be put off for any period greater than a week, this will keep your recollection of a purchase or sale clear so accurate recording is possible... put off for too long, you could forget what a receipt was for and which job it applied to.

Your records are a pulse of your business, monitoring how your business is developing and where your customers are coming from is vital to developing future plans and goals.  Keeping record of jobs that had to be declined and the reasons why, will help you to develop expansion plans and plot the purchase of new equipment.  Knowing which products are consumed in what time frame can be a time saver when you notice that certain stock is used repetitiously, you might find savings in purchasing larger quantities of stock that has shown a steady consumption pattern.

Keeping good records is as important as knowing good design and layout, and is just as much a part of your business as the software and paper stock you have on hand.