Questions : Selling here for the first time

If you are in the US, only sell to a US location at first. It simplifies things greatly. I typically ship FedEx Home Ground. It is usually the least expensive. It may be a bit less expensive if you have a FedEx Account. Insure for the full sales price and require an adult signature.

Always over package your items. Sometime even the original factory inner packaging material is inadequate. Add more packaging if needed and double-box when possible.

It’s definitely more convenient, less risk, and less cost to ship within the continental USA. I generally sell USA only, but sometimes certain big-ticket items (e.g extremely un-obtainum OOP high-end headphones) are much more highly in demand in Asia/China, and that makes it tempting.

That said, once you get packages over a certain size and weight (and you will often end up with big packages if you’re packing properly), it can be surprising how much it costs to ship ground from one US coast to the other.

And prepare yourself for an absurd onslaught of "why are you selling?" questions, lolz. A couple times now I’ve gotten tired of the tire kickers, gave up on the ad, and later became thankful I never sold that piece (i.e. further tweaks, additional burn-in, changed system balance, etc)! When I want to buy something, I know I want it -- so I offer a generous/fair price right off the bat (often asking $) and avoid the BS -- purchases go very smoothly this way. But a LOT of buyers here want to feel like they "bargained down", regardless of the start/end price, so you might consider padding your initial ask price to account for this. Stupid habits, if you ask me. 

Shop around for best shipping price. Pretty sure UPS stores are independent so the owner may try to gouge. I've walked after given a price and saved $30 at another location (FedEx).
Be very specific (and truthful) when writing your ad. If anything is wrong with your item (scratches, dents, etc.) say so. If you have a "no returns" policy, say so and try to get the buyer to inspect and accept ASAP (and get it in writing).

The best method of shipping is FedEx Overnight. Second best is USPS Express and USPS Priority. Never ship ground anything, they may be able to find a way to break even unbreakable items. Why take more risk than needed? Any shipping is risky.
What are you planning to sell ?
Don't get offended by low offers. Before the sale is done your item is worth zero. Just ignore truly ridiculous offers. I can see many ads here of overpriced pieces, and it is in most cases the buyer's market now.
Post clear pictures of what you sell, the more the better, including the back of the equipment and serial #.
Buyers do take a risk too, even more, they send you money and for a while they got neither money nor the item they bought. Their anxiety is understandable and should be acknowledged. They should have a certain level of trust to buy from you.