Anything to be careful about on a first visit?

The short answer is that almost nothing needs bracing for. Two things must be kept. One: be in your seat by curtain time. Kabuki acts often open quietly, and a latecomer may be held by the staff until a suitable point to enter. Two: do not photograph or record during the performance. This concerns copyright and the performers' rights, and every theatre states it plainly.

Beyond that, much of it is simply to be enjoyed. At the interval you may eat at your seat; theatres sell bentō made for the purpose, and some people come partly for them. There is time to browse the shops and look at the displays. Rent the earphone guide and commentary comes to your ear. Kabuki theatres have been receiving first-time audiences for generations, and every piece of guidance you need is inside the building.

Two practical notes: the day is long, so use the intervals for the washroom; and during the acts, watch only for chatter and phone light — a screen is far more conspicuous in a dark house than one expects. And finally, the thing most worth saying: it is fine if a scene loses you. It loses the regulars too, and people who have gone for decades still notice new things. All that has happened is that you have gained one more reason to come back.