Do this before removing the sprayer's dust cover to prevent accidental spraying. You do this for the same reason you may shake a juice before drinking it. Liquid mixtures sometimes separate a bit, and shaking ensures an even distribution of ingredients. This is especially important with medication. Remove the sprayer's dust cover after shaking the bottle. To use it for the first time or after not having used it for a week or more, you must prime the Flonase bottle. Hold the pump applicator vertically between your forefinger and middle finger. The bottom of the bottle should be supported by your thumb. Point the spray nozzle away from your face and body.  The very first time you use a new bottle, press down on the pump six times to let off pressure. To re-prime a bottle you've used before, press down and release the pump until you see a fine spray. Before using the nasal spray, you need to clear your nasal passages. Otherwise, the medication might get caught in the front of the nostril, where it will be less effective. Blow your nose until you have completely cleared your nostrils. Do not blow your nose after using the spray. Lean your head slightly forward and carefully place the nasal applicator into one nostril. Be sure to keep the bottle upright, and hold the other nostril closed with a finger. You should be holding the pump with the applicator between your forefinger and middle finger, and the bottom supported by your thumb. Breathe in through your nose while pressing the pump to spray the drug into your nostril. Take a normal breath in through that nostril, but breathe out through your mouth. This prevents you from blowing the medication back out through your nose. Repeat the steps in the other nostril. Improper hygiene can increase the chances of infection with repeated usage. Every time you finish using the applicator, wipe it with a clean tissue and replace the dust cover. At least once a week, you should clean your nasal spray applicator with warm water. Remove the cap, then pull on the applicator...

How would you rephrase that briefly using Vietnamese?
Lắc nhẹ chai xịt. Bơm mồi nếu cần thiết. Xì mũi. Đặt đầu chai thuốc vào lỗ mũi. Bơm thuốc. Giữ sạch chai thuốc.