Others have already mentioned the prohibition against "mystery boxes/lots" Do some research both here and on other sites to get an idea of what similar items have sold for. If they are "unique" and you are unable to find any references I would suggest using the auction format and set the starting bid price at the least you are willing to take from the item. Some buyers like bundled items, some are looking for singles depending on what you are selling. There is no one optimal method or format.
You are a new seller I would suggest you avoid using best offer and list a few lower cost items until you get some experience and feedback built up. Depending on what you are selling you may possibly be a prime target for every scammer out there.
Make sure you FULLY understand the eBay money back guarantee and the fact that as a seller you have little to no protection from the scammers. Understand that "buyer does not accept returns" does NOT translate to no refunds and eBay's policies generally mean little in the face of a NAD chargeback.
Fully understand the eBay fees and how they are applied and factor those into your cost model along with your other selling expenses including Federal and State income taxes. This is especially true when it comes to shipping costs and options. The buyer should always be paying for shipping regardless of whether you use calculated shipping or free shipping and factor the shipping cost into your price.
EBay is NOT for selling everything despite what some believe. Some items are better sold on local forums especially high dollar items, large heavy items or fragile items.
