How can we prevent Sinusitis?

Nasya - usage of Oil (pure ayurvedic (Shadbindu Tel or Gingelly Oil) drops to soothe and protect the nasal passages to relieve sinus congestion.
But ready fully about Nasya and only then practice it.

Nasal irrigation using the Neti pot

Pranayama - Breathing yoga excercises

All these techniques hardly take time or money to practice. They not only prevent, they CURE Sinusitis. Takes some time in some cases but be patient. You can follow any one of these or all.

Read up on them, completely understand them and take it step by step. Do whichever is comfortable to you.

So read my other answers if your sinus is chronic or has been there for more than six months for a holistic solution.

Off late i also found something called Salt room therapy. While relaxing in one of treatment rooms, customers inhale the dry, salt-enriched air deep down into the lungs, where the healing benefits do their greatest healing. The salt loosens the mucus, which begins to clear quickly, and inflammation is reduced, which makes more room in the airways for you to breathe. Symptoms subside, sometimes for up to 12 months.

Dry salt air is more powerful than moist air. The negatively charged ions in salt improve our health and mood. Inhaling particles may reduce inflammation and mucus in the lungs, improving most respiratory conditions such as asthma, allergies, bronchitis, sinus congestion and Chronic Obstructive Pulmonary Disease (COPD).

See if you have it nearby or see if you can customize, like use a nebulizer at home. BUT MAKE SURE YOU KNOW HOW TO PREPARE THE RIGHT SALT WATER OR SALINE SOLUTION. PLUS ENSURE ITS HYGENIC AND YOU HAVE CONSULTED A DOCTOR WHILE CUSTOMIZING YOUR SALT ROOM THERAPY USING A NEBULIZER AT HOME.