If you're really serious, I'll throw some pointers out there. Ive owned 2 online stores in the past (paintball related), so I've shipped thousands of packages.
Don't skimp on packing materials and tape. ASSUME the carrier of your choice is going to throw it off a building. Use plenty of bubble wrap, peanuts, etc and don't skimp when taping the box.
Always insure the package for full value. If you need to file a claim, you MUST show proof of receipt for that value. And if you ship USPS, pay the extra for delivery confirmation.
And always ship the next day AT THE LATEST. Nothing ****es somebody off more that paying for an item and you not shipping it for 3 days.
Lastly, I always typed the buyers address and my return address in Word on the computer. Some people have sloppy handwritting, and a typed address eliminates any confusion. Then tape over the entire label. If the label were to get wet en route, this prevents any smudging.