New skis will be dirty from the manufacturing process and have a layer of factory wax.
NOTE: Never use base cleaners on your base. Always clean by the hot-wax-scrape method. It is good for your base and repeated waxing keeps the bases running fast.
Scrape the factory wax off with a plexiglass scraper.
Use the hot-wax-scrape method to completely clean the ski.
Choose an inexpensive soft (warm-temperature) wax. The red (warm) hydrocarbon wax (PB-1000) sold here is excellent for this purpose.
Set your skis in a vise and hold the brakes back with a brake retainer.
Iron on a coat of wax and scrape it off while it is still liquid. You may see dirt or grime in the hot wax.
Repeat waxing/scraping until the wax is clean.
If the ski conditions are cold, start with a warm wax to clean, but switch to a cold at the end. The idea is to a warm wax that will stay fluid longer and penetrate deeper, then transition to a wax that more closely matches your snow conditions.
Allow to cool at room temperature.
Follow up with a brass brush; leave as is if you are done for the day.
Check for flatness
Hold a true bar to the ski at 8-10 points along its length (see picture below).
You are looking for a base that is consistent along its length, neither high nor low compared to the edges.
Base material should be free of waves.
Add structure to your base
The average skier may wish to retain the factory grind; a racer should consult with a shop technician that knows what grind is performing well in your region.
For a new ski to be stone ground by a technician, consult with them to select the best structure for your snow conditions.