ALL the good brass players I know had good teachers. You need a good teacher right from the start, even if you only have a couple of lessons to learn the basics. Do it yourself and you could do yourself so much damage that you never succeed.

Those who have succeeded without a teacher have done so despite it, not because of it (and there aren't many of those around. It isn't like some other instruments where you can fiddle around and in time it will work and you'll manage something and may even get good, if you damage your muscles at the start you'll never recover