If you have Ayaka and you want to ascend her, then you will need a lot of Sakura Blooms. It can also be used for various new cooking recipes. Here are the farming routes that you can follow to harvest Sakura Bloom every 48 hours (from pickup).
Remember that Sakura Blooms can only be picked up after they come in contact with Electro, similar to Dandelion Seeds.
See all item locations in the Teyvat Interactive Map.
If you want a video demonstration, hope this guide will help you get Sakura Bloom easily.
You can also check this guide if you want to farm Naku Weeds and start preparing for Yoimiya.