There are many famous cherry blossom viewing spots all over Japan, which are featured in many guidebooks. However, the time of full bloom of the cherry blossoms varies depending on the region and climate, and you can only enjoy the blossoms for a short period of time: about one week after the blossoms are in full bloom (depending on the type of cherry tree). The websites of famous cherry blossom viewing spots also provide information on when the blossoms will be in full bloom, so make sure to check them out.
Everyone present is there to enjoy cherry blossom viewing. Please do not break the branches of the cherry trees, take your trash home with you, and do not enter off-limits areas, among other manners.