To improve the mileage of the Royal Enfield Bullet 350 Military Red, ensure regular maintenance such as changing the oil filter, air filter, and engine oil as recommended. Maintaining the optimal tire pressure and avoiding excessive idling can also enhance fuel efficiency. Additionally, driving at moderate speeds and using the correct gear can help optimize mileage. The Bullet 350 already offers a certified mileage of 37 kmpl, but owner reports suggest it can achieve up to 38 kmpl with proper care and driving habits.