Drink lots of water
Just like in all sports, staying hydrated is one of the most important things in ITG. I stress this point because it's important to see that competitive dance games are just as athletic as other more conventional sports. Runners need to drink water to stay hydrated, and dance gamers too.
Drinking helps you maintain a consistent body temperature and help lubricate the joints, as well as help transport nutrients around the body. It helps prevent muscle cramps and spasms, and avoid dizziness and nausea from dehydration.
Dance gamers especially need to drink water as they play because of the high volume repetitive movements that they undergo and the lack of motion and subsequent lack of wind flow accelerates temperature body growth increases. We usually play with fans trained on us or some sort of cooling to help control this, but drinking something is always the best way.
You can't just drink anything
Since the primary demographic of dance game players are still video gamers, lots of them like to drink carbonated drinks or sugary drinks whilst they play. Not only is this bad generally, but it provides uneven levels of energy and the artificial flavorings and additives can impede proper energy flow.
It's still common to see people drinking energy drinks whilst they play, and I often see them or sometimes even 1.25L bottles of soda being chugged in between songs. I could never see myself drinking something like that whilst I play. I prefer to drink room temperature water (chilled can be more difficult to swallow), or occasionally a pulpy orange juice for something with more substance.
I always like to drink water between songs, but sometimes I take it during a song if it is long or there's a break that affords me an opportunity to, but there have been times when I was caught out and stray arrows started scrolling by without me being ready to, and I would fail the song for it!