My experience (limited though it is) is that you just need to get out there and do it. If you’ve got an understanding of principles of camouflage and why things are seen and you keep all those annoying throw away lines in mind you’ve pretty much got everything I’ve ever read of use on the subject. Getting to spend time in the scrub with someone who knows the game well is invaluable, but not necessary.
A game you can play with friends (we do it at work from time to time) is to select a dense bit of bush somewhere, define an appropriately sized movement box (for 1 or 2 people per team it may only be the size of a couple of basketball courts) and try to move from one side of the box to the other while the other team is doing the same from the other side. You can use air rifles or just a handful of rocks, but you’re trying to get through unseen and unheard, while pinging any bad guys you see. Once you’re hit you’re ‘dead’. We often apply rules like you can’t stay still for more than 30 seconds to keep guys trying to move quietly, otherwise you just get a bunch of guys waiting in ambush.
The best part, and the real learning curve comes at the end when you hear from your ‘enemy’ how they found you.
Mr Alex Bugnon summed up everything anyone has ever taught me on the subject quite nicely somewhere on this forum. To paraphrase: “Watch a cat stalk a bird and believe you can move like that”. 😉