Let it run for 15 minuets with the drain valve in the bottom of tank open, so that the tank won't hold air. once that is done, just close the drain valve and let it fill with air. You break an air compressor in so that all the moving parts have a chance to properly seat before actual usage.
It depends upon whether you have an oil filled compressor or a dry compressor. The dry compressors are basically ready to go. Just open the drain valve, run a few minutes to get up to temp, close the drain valve, and remember to open it again after you've used it the first time, and you're done. The oil filled units are usually fill with oil, run two or three minutes with the drain open to get up to operating temp, dump the oil, and refill. Then you're ready to go just like a dry unit.