As I'm sure you all know, accuracy is usually the number one challenge for horn players as we strive to skip our way through the maze of French horn harmonics.
I was recently given an exercise by my private instructor that has made a significant improvement in my accuracy because it trains my ear to hear & my lips to feel the subtle differences between major & minor thirds & the triads that can be built with them.
If you're a beginner you may need some help from your teacher to help you figure out what all this means, and you may also have to adjust it to fit your range (one octave instead of two; fewer scales, etc.), but I'm sure that once you start working with this, your accuracy & confidence will improve as mine did.
This is how I do it: Play a 2 octave C major scale (starting on low C) from bottom to top to bottom. Then play C major triad(arpeggio)w/i the same octave(s) range -- bottom to top to bottom (C,E,G,c,e,g,c,g,e,c,G,E,C). Next play the c minor triad (arpeggio)in the same manner (C,Eb,G,c,eb,g,c,g,eb,c,G,Eb,C). Now here's the hard part: play a c diminished arpeggio (C,Eb,Gb,A,c,eb,gb,a,c,a,gb,eb,c,A,Gb,Eb,C).
My instructor has me doing this in every key going up chromatically from low C to B just below middle C. It's a HUGE challenge, especially in the beginning. The first week I worked on it, it took me an hour to get through it. I had to write out the notes for the diminished arpeggios in every key, but I'm so glad I put in the time. The pay off is worth it. W/i days of starting this, I played with a lot more accuracy & confidence in band practice & our Christmas concert.
Get help from you band director or instructor to adjust it to your abilities.