i sell online. definitely get a scale so you know the weight range. the USPS website has a shipping calculator now. i use my zip and a zip in the furthest zone from me to get a high estimate to avoid surprises. The shipping calculator on USPS.com does not provide as many options as the ebay calculator. To see everything, i keep an old sale visible then pretend as if i am going to print another label to open the ebay shipping options window.
the BOTTOM line is most important to me so i keep all my shipping options open. I list ALL my items as shipping FREE ECONOMY with an option to ship Priority upgraded buyer paid. I ship 2 day (since ebay removed the incentives to ship faster). This allows me flexibility to choose the best shipping option for my bottom line.
1st class shipping is cheapest overall if under 16oz. i make every effort to ship 1st class when weight allows. SmartPost (a USPS/FedEx hybrid) is the next cheapest, slower. Use your own boxes for SmartPost. My last option is Priority. Note that there is also a Regional Flat Rate service that can work out better that Regular flat rate. The regional flat rate boxes are also a bit bigger. I am an origami expert now! MAKE IT FIT if it won't break or destroy your items over 1 pound.
Bubble wrap is a must. I swear by tyvek envelopes (super lightweight). I avoid boxes where possible. AND YES, get all the USPS shops you can. I am overjoyed when a shop coincides with a sale!
i hope i could help. happy selling