Well, a "relaxed touch" is not exactly what it sounds like. Relaxation, firstly, isn't just in the hands/fingers, but something within the whole body, involving joint alignment and balanced posture, extending into the arms and hands and fingers. However, playing the piano is not truly about just being "relaxed" and balanced, but rather about tension and release, as well as clearly defined mental intentions and physical motions. Also, learning how to kinesthetically feel tension within parts of your body at any given time, learning what motions tend to create tension in general for you, all of this is not something that is achieved once and then you never have to think about it again. Yes, habits do form and some things that you had to make conscious efforts about at one point may become second nature to you after awhile, but there is always more to go.
Personally, I have explored a few different things as it relates to finding balance and tension-free playing (and I am still discovering). I learned quite a bit by reading Thomas Mark's book, "What every Pianist Needs to Know About the Body" and applying and experimenting with ideas in that. What I took mostly from that book was how to sit in a balanced way, and a mental assurance that we are indeed actually built to sit and should be capable of sitting at the piano for hours without pain. Eventually that morphed into something else though, as while I was first learning about it, I had to discover just what it felt like to be balanced and aligned. I couldn't do all of my playing like that though, and had to discover how to move when I needed to and then either come back to a center, or find nearly the same kind of tension-free feeling, even when my posture might have changed.
I also spent at least a year completely reworking my entire technique with "forearm rotations," part of the big idea during that time being joint alignment within my body vs. alignment with the keys. Eventually that also morphed into something different, as now I do make a point of aligning with the keys, but had to find a way to do that while experiencing the same kind of tension-free feeling as when I was working on just aligning my joints regardless of how I aligned with the keys.
After that, I once again completely reworked my technique under the guidance of a watchful and knowledgeable teacher. There is A LOT that I can't put in this post, simply because it's too hard to try to write it all out, and even if I could it would probably be completely overkill.
Regarding "relaxation," I think the most important thing along those lines that I have been learning in my current work is that relaxation isn't just an isolated idea, and if it's treated that way then the musical concept will suffer in its realization (similarly to how the musical concept would suffer if there is unreleased tension). I am learning that 'tension and release' is directly tied to musical concepts and pianistic motions, and that it all comes together to create a complete package during performance.
Topic: Playing with a relaxed touch