I've done a little bit of work with junior bands, and I play sax in a concert band, so this is based on my experience there.
The first step to playing in tune is to know when you are out of tune. A tuner is one way to get this information. But it's not ideal for a couple of reasons. For a start, most tuners that I have encountered use equal temperament. Concert bands (and I assume brass bands) often use just intonation. The tuning of a note will subtly change depending on what role that note plays in the overall chord. This took me some time to get my head around.
Another issue is that the tuner is probably fixed to a 440Hz reference. Whilst that's usually our target, it's more important that the whole band plays in tune with each other. Even if the fixed reference is off.
Finally, if you're spending you time staring at a tuner, you're probably not paying attention to the conductor, the music, your tone, etcetera. It's another potential distraction.
So, to your actual question. How can you get better at playing in tune? Here's some thoughts:
- Know what it sounds like when you are out of tune. You should be able to hear a beating sound when you're out. If you don't know what this sounds like, ask someone to demonstrate.
- Know where your particular instrument has intonation issues. I know that on sax, my C# will need attention, and my high A also tends to be out. This requires personal practice, probably with a tuner or other reference source.
- Practice playing in tune as a band. At the end of the day, the band needs to be in tune, not each individual player. In fact, if everyone plays perfectly in tune according to a tuner, it's not going to sound as good. Why? Equal Temperament and Just Intonation again. If you've ever had someone tell you to play thirds a bit flat, and fifths a whisker sharp, they're asking you to play using Just Intonation.
As an extension of the question, here's some exercises that we use to work on tuning in a band context:
- Scales. Let's start with the obvious one. A tuning scale is better than a tuning note, because intonation changes as you change notes. You need to subconsciously adjust. Don't just use Bb major; different scales present different tuning challenges. F major gets quite high. Unfamiliar keys are often harder to keep in tune, so practice them.
- More scales. Let me expand. We'll do exercisee involving singing a scale interval, and then playing it. The idea is to make sure that you actually know where you are aiming before you try and play it. I'm not a great singer, but the idea is to hear the pitch you are aiming for before you try and play it.
- Scales and chords. Have half the band start on the first note, half on the third, and half on the fifth. Play up the scale, and you'll get the diatonic chords. Play them in tune. Or, instead of the playing the same scale, play three different ones. A third of the band plays Bb major, another third plays D major, and the rest play F major. You'll get a different set of chords. Again, do this slowly, and play in tune. Don't move to the next note until you've got the previous one right. Don't be afraid to go back to the beginning if it gets out if hand.
- More chords. We often do and exercise we call a 1-3-5-8. Pick a scale. Then, everyone picks a number: 1, 3, 5, or 8. Everyone starts at the root of the scale, and we got up it. When you get to the scale degree that matches your number, you stay there until the rest of the players get to the top, and then come back down again to meet you. So the first note, everyone will be on 1. Then, 1+2, 1+3, 1+3+4, 1+3+5, 1+3+5+6, 1+3+5+7, 1+3+5+8. On the way down, the reverse happens.
I may add to this list, but that's a start. My point is that playing on tune needs to be a whole band thing as much as an individual thing, so you should spend time practicing it as a band. It's the best way I've found to train my ears. Individual practice is required, but it's not sufficient for the entire band to be in tune. Corporate practice is required as well.