If you're making slabs, the one tool you must have is a spring steel scraper. Don't try to make do with a credit card, or something you find in a hardware store. Buy a scraper! This scraper costs $2.79 at my pottery supply store, and I pick one up every time I stop in. Scraping preps the slab, compresses the clay, and pushes the grog into the slab. Become a "Master-Scraper" and your finished work will be so much better.