After purchasing a wooden instrument of any kind care must be taken to protect it from extremes in temperatures and humidity.

Never leave your instrument closed in a vehicle especially in summer or winter. Wood is very sensitive to changes in humidity and warping can effect the performance and sound of your instrument.

Where possible, it's good practice to store your instrument in a case or bag in a general living area rather than an attic, basement or cellar.

You can further protect it by periodically oiling (if already oil finished) with linseed oil, available from any hardware store. Allow 30 minutes for the oil to penetrate before wiping off. The oil will take 24 hours to cure after which you may buff with a soft cloth for a natural luster and sheen.

Before finishing your new shell you should raise the grain to make the shell ultra smooth and to prevent the grain from raising during the finishing process.
To do this, wipe the outside of the shell with a damp rag. Once it's fully dried lightly sand it with 220 grit, just enough to knock off the fuzz that the water raised.
Now you are ready to apply the finish of your choice.