Hi, I ordered a book blowgun technique, but meanwhile I need help with breathing technique, how to shoot, how to aim.... Simply basics, I know there are videos on YouTube, but I dont want to develope bad technique, so maybe You Can give me a links on what is worth watching. Thanks!

I never shot a blowgun, so I can't really point you in the right direction.  There are a couple blowgun shooters who pop in here once in a while.  Maybe they'll be able to give you some good advise.

I can give you some general advise though.  I wouldn't worry too much about developing bad technique at the beginning.  For most things, the beginning is going to be bad technique no matter what you do.  The important thing is to be able to make adjustments when things aren't working well.  I think it would be worthwhile to check out a couple random videos on YT, give things a try, and see if certain techniques work for you.  In the world of primitive weapons, a lot of things are experimentation, self-learning, and rediscovery.

You don't want a 'drawn-out' exhale - pppppppppp
A full lung 'dump' in a short sharp puff - huh!  Use your diaphram to 'spit' the breath up and out.

My method
https://youtube.com/shorts/EzxJgFvHNy8?feature=share

I have always enjoyed the method I learned  with the old jivaro blowguns and that is as has been a full burst or lung dump. But! One must continue to put air behind the dart until the dart leaves the barrel. Especially with the longer guns or you just don't get the full potential of the longer guns. Yes this does take practice and lung exercise. Definitely worth it.