You want to do that once or twice to get all the crap out of the bottoms of your skis. Then you want to leave one coat on overnight, and scrape it in the morning. Some people just ski the wax off the next day insted of scraping it off, but thats not very good for your bases, especailly if you are using cold wax. Then again, if you are hitting rails it probably doesn't matter much.
And your scraper would be plasitc or in some cases metal, not rubber.
I will try to get a more detailed post on tuning up sometime, but no promises.