Invest in a waterproof case that fully encloses your phone. Waterproof cases create a barrier against moisture and are essential if you expect heavy rain or plan to be near water bodies.
If you don't have a waterproof case, a sealable plastic bag can provide temporary protection. Zip-lock bags or specialized waterproof pouches are also specially designed for phones which gives protection against water.
Keep your phone away from direct exposure to rain as much as possible. Use an umbrella, Rain coat, or any form of cover to shield your device from getting wet.
A good quality screen protector won't make your phone waterproof, but it can help protect water droplets from accumulating on the screen.
If you're not actively using your phone in the rain, consider turning it off or putting it in airplane mode. Due to this the risk from water damage get reduced and battery life get extended.
After exposure to rain, dry your phone thoroughly with a soft, absorbent cloth. Pay attention to ports, speakers, and any openings where water might seep in.
Regularly back up your data to a cloud service or computer. In case of water damage or other mishaps, having a backup ensures you don't lose important information.