Hello @Zekroma and welcome to Blenderartists !
Well, the method varies depending on what is the input data. For a curve it’s simple since it’s just a matter of knowing the curve’s segments length, add those and feed that to an axis ( X, Y or Z) depending how you’d like the curve to be. I don’t recall exactly what I did back then, but it’s probably using the accumulate field node to add each segment’s length.
When your input is some instances, like in my flower project, it’s likely to be even more simple since the data is already there, there are some nodes like Instance Rotation, Location , Scale, Transform… and it’s just a matter of subtracting location, inverting rotation …
When your input is some faces… well it’s a bit more difficult and from what I recall I didn’t managed to have a method that worked on everything so I did a few “passes” to cancel the rotation. At least since we have the face’s normal it’s easy to align the face’s toward something, by reversing an align vector to euler. Now for the other axis it’s not perfect, if the face corner’s are 90° then it’s possible to take an edge and use that as an axis…
Anyway, I managed it eventually but I had a bit of luck I think 
I hope that helps you to get an idea, most of the time when doing GN stuff I found that it’s rare that there is a general technique that works everywhere, but rather the technique is always specific and based on what your input data has to offer…
Well, not to my knowledge but I must admit that I didn’t look that much tutorials in the last 2/3 years.
Anyway it’s worth experimenting with that technique on simple cases and eventually it can become a second nature !