1. Use a proper embouchure. An incorrect embouchure can put strain on your lips, jaw, and throat, leading to fatigue. Make sure your lips are relaxed, your jaw is not too tight, and your teeth are not clenched.
2. Take breaks. It's important to take regular breaks when practicing the French horn. This will give your muscles and lungs a chance to rest and avoid overexertion.
3. Do warm-up exercises. Warming up before you play will help to prepare your muscles and prevent injuries. There are many different warm-up exercises available online and in music education books.
4. Stay hydrated. Drinking plenty of water will help to keep your muscles hydrated and prevent them from fatiguing.
5. Use a supportive hand position. The way you hold the French horn can affect how tired you get. Make sure your hand is positioned comfortably and that you're not gripping the horn too tightly.
6. Practice regularly. The more you practice, the stronger your muscles will become and the less tired you'll get. Try to practice for a few minutes each day, and gradually increase your practice time as you get more comfortable.
7. Take lessons from a qualified teacher. A good teacher can help you to develop a proper technique and avoid bad habits that can lead to fatigue.
By following these tips, you can help to reduce fatigue and play the French horn for longer periods of time.