Star,
I'm not sure what kind of business you are doing or whether you are selling on ebay or not, but a word of caution if you are selling on ebay. Watch their fees very closely. When they offer "free insertion" offers or No fee's for the first 5 listings, their %'s on sales change. You think you are making out, but in reality, you very often are actually paying more in fees! You need to calculate those increases into your handling charges. I have found also, that when I began advertising shipping within 24 hours of receiving payment, my sales can actually go up because folks are willing to pay for fast shipping and will leave really great feedback when they get their merchandise quickly.
I love using paypal and ebay and made myself a flowchart to keep track of expenses (especially when I started selling for others). Good luck!
Sharon