Is there a trick to clean blackstone?

Clean it while it's still hot. Scrape the food off, squirt some water on and it steams the stuck bits loose, scrape again, wipe, then a thin coat of oil before you put the lid on. If it's gone rusty, scrub the rust off with a grill stone or steel wool, wipe it clean and re-season with a few thin layers of oil heated until it stops smoking.