1) Inspect it before you let the delivery driver return to the yard. Many of these containers have holes/cracks in the top and/or the doors don't operate well. Insist on one that's in good shape when you get it.
2) Place it on a hard, quick-drying level surface when it arrives. . . or have some high-capacity, high lift jacks/forklift handy to pick it up so you can get it out of the mud and place it on some piers. While you have the lifting gear deployed, shim it to get it level or sloped slightly toward the 'door' end for drainage. Containers are mostly sheet metal and will rust out amazingly fast in contact with the soil or if they're sitting in a puddle. Too, the plywood bottoms will rot if they can't breathe/drain. (like rot completely in 2-3 years!) Also, if you're wanting to put shelves, etc. inside, a mostly-level floor will be important.
3) containers are a commodity-- call around to the various freight forwarders and look in the phone-book. Prices do vary, as does the level of service at delivery time. Some outfits will do all the leveling, piers, etc., as part of the package-- an "installation, if you will. Others do not-- they'll plop and run, sometimes without even getting a signature.
Be up front about it. . . find out what they offer, and what extra-fare services are available; and tell them what your expectations are. $200 extra to have the thing put on piers and leveled is a bargain, in my opinion. Prices may have gone up in the last 10 years, so don't take that as a market rate! Your milage may vary, of course. . .