Scrape around the cracks with a putty knife, and use a paintbrush to clean off any dust. Be sure to wear safety glasses when cleaning the ceiling.
Fix large cracks with joint compound before you use the textured patching compound. If the ceiling has water damage, apply a coat of primer/sealer before you use the patching compound.
Apply the patching compound by dabbing it onto the ceiling with a small paintbrush. Use only a small amount of compound. For corners where the textured ceiling meets a smooth wall, wedge a large flat object such as a broad knife into the corner to prevent patching compound from getting on the wall.