You get active
Naturally, the first thing that living a dance game life does for you is that it gets you up and moving. You hit arrows with your feet, and at the highest levels of play that becomes more of an athlethic activity than may outwardly seem.
It can be a real drag at first pulling yourself onto your feet and actually playing. As a footspeed and stamina player, it's pretty daunting going back into training for ITG because it means needing to play on a regular basis, or at the very least be active on a regular basis. I have to hit loads of arrows and train multiple times per week to ensure that I'm not just maintaining my abilities but growing them as well.
I take a methodical approach
There are lots of different ways to train, but the most obvious is to simply play. By playing alot, you're exposing your body to the stresses of playing so that it can recover and become stronger.
I have a tendency to overtrain when playing, but it does result in fantastically rapid and intense gains. I'm known for maintaining a very high level of play whilst off-season and haven't really gotten back on-season for a couple of years, which means that my peak performance at full ability is likely to be even higher than I'm currently aware of.
Another thing I like to do is cross-train by running and lifting weights. Running is good, but sometimes it clashes with direct training since all the stresses are focused on the lower half of the body, but I do take a chunk off playing sometimes and just run alot to help improve my cardiovascular endurance and help consolidate my ability to persevere whilst in a constant state of physical stress. It's a bit like becoming desensitized to the pain so one can bring out their energy with that stress as the performance baseline. In other words, making it feel like there is no stress happening at all. I believe that stamina is largely a stress-management game, and new ability largely stems from the ability to mitigate pain, whilst only a portion of it comes from actual new muscular growth.