Please tell me the precautions after fluoride application.

For 30 minutes to an hour after fluoride application, do not eat or drink anything, including water, so the fluoride is fully absorbed by the teeth. Swallowing saliva is fine. Avoid carbonated drinks and sticky snacks for the rest of the day; brushing is usually fine from that evening. Fluoride application is not a one-time measure - having it regularly every 3 to 6 months is what helps prevent cavities.