There are agile practices though. Some of them are so simple we don't even think of them as being a practice.
Practices like continuous integration and unit testing traditionally fell into that category. I would say these days that writing unit tests is so common that it doesn't feel like it came from anywhere. Just that it always existed.
I think the important thing to keep in mind is that while Agile principles may sometimes be commonly well served by certain sets of practices or processes, the practices/processes themselves are usually not Agile (except for the high-level process of evaluating and selecting processes -- Agile is about choosing the process that works for the actual set of people you have, not about choosing process based on considerations outside of the work groups ability to produce quality software.)
The ossification of Agile into a set of cargo cult practices divorced from the particular teams and their needs flips Agile into exactly what it was a reaction against.
In my experience the main thing to keep in mind to improving any system is to:
1. See what state you are in
2. Figure out what new state you would like to be in
3. Guess at something that will help you move into that state and then follow that guess.
4. See if that move helped you get closer to that state
5. goto 1
People label those steps with lots of names depending on what industry they work in but in the end that is the easiest way to get better.
Practices like continuous integration and unit testing traditionally fell into that category. I would say these days that writing unit tests is so common that it doesn't feel like it came from anywhere. Just that it always existed.