Do a search on ebay to see what similar items are selling for. If it's something there is a lot of, do a search, and then sort it by price - highest to lowest, and see what the magic number is that people are bidding at. If there are 10 items, ranging from $0.99 to $10, but there are only bids at $5, then $5 is a safe place to start.
You can choose to set a flat rate, or let the ebay calculator figure postage -you just put in what the weight of the package will be, your zip, and what type of shipping (USPS Priority, Media Mail, Parcel Post, UPS, FED-EX, DHL etc). When the person bids, it will figure what the shipping will be from you to them, using the type of delivery you chose to use. I always put in the listing that I will be using X type of shipping, and if they buyer chooses different, they have to pay any extra costs.
I personally restrict bids from people with 0 feedback or multiple negatives. I don't need any nigerian scammers

I also state in my auction that insurance, deliver confirmation etc are NOT included, and if the bidder wants that, they have to ask for it. My PO gives me a receipt with the zip code of each package on it, so I have proof that I send it out, though I've never needed it.
Also, take good pictures!