For most large format prints with close viewing distances the raster image components should be 100ppi at the print size. Hard-edged raster components (e.g. text done in Photoshop) can be up to 200 ppi at the print size. For longer viewing distance banners and signs you can go lower without any visible difference.
Small format prints such as flyers and brochures should have the raster components at 300ppi.