I feel that the key to learning any brass instrument - in my case the tuba - is building up a good warm-up routine.  This is an idea that has been passed on by all of my teachers and which I believe has the greatest impact on any musician's development.  A warm-up of 30 minutes each day to me is equivalent to that of a runner before they set off for a marathon.  You would not expect the runner to set off without due preparation and the same goes for musicians.  To play an instrument you have to use your muscles and as such warm up because you are embarking on a physical exercise.  A repeated routine which strips down as many different areas of your playing as possible will help your intonation, make you more familiar and therefore confident and imprint in you muscular memory - you will remember where notes are as well as being able to hear them.  By practising scales, slurs, long notes and short notes in isolation, you are preparing yourself for the practice ahead and obtaining the tools you need to tackle anything you want to play.