The most honest part of the answer first: you do not need to prepare. The first class is built for someone who has done nothing, and nobody expects anything else. People who wait until they are in shape often wait a year and never arrive.
But if you are going to prepare anyway - because it makes the step easier, because you like having something in hand first - then it is worth knowing what genuinely makes a difference in a month and what is wasted effort.
What will actually surprise you
Not your fitness. An hour of Kung Fu is not a running load, and most people cope with the conditioning without trouble.
What will surprise you is three other things. Hips that do not open as far as a stance requires. Inner thighs that ache for three days after the first session. And ankles that, after twenty years in shoes, no longer know how to balance on a bare floor.
All three can be measurably improved in a month, and that is the point of preparing, if you choose to.
Four things that help
Supported deep squat. Hold a door handle or a table, drop into a deep squat with heels down, and hold for thirty seconds. Three times. This is the fastest route to open hips and ankles and the one exercise on this list that is genuinely essential.
Standing on one leg. Barefoot, thirty seconds each side. Once that is easy, close your eyes - and discover that it is not. Balance improves faster than anything else, usually within two weeks.
Walking barefoot. Take your slippers off at home. Nothing else. A foot that has worked on its own for a month is far less shocked in a first class.
Wall sit. Back against a wall, slide down as if sitting on a chair, knees above ankles. Hold as long as you can - twenty seconds the first time. By the end of the month it will be a minute.
Ten minutes a day, four weeks. More is not needed and more will not help.
Three things that do not help
Running. If you do not run, do not start now. Kung Fu is not endurance training and running will not prepare you for any of what is coming. If you already run, of course carry on.
Abdominal exercises. The core matters in Kung Fu, but it is trained standing and under load, not by curling up on the floor. A hundred sit-ups a day will give you nothing in the first hour.
Watching technique videos. Memorising a movement you have never performed does not work, and there is a risk of arriving with a picture that has to be dismantled first. An empty head is an advantage in a first class.
What about flexibility for kicks
This is the most common question and the answer is reassuring: high kicks are not a requirement for anything. We work with low kicks most of the time, and anyone who never lifts a leg above the waist in their first year misses nothing important.
Flexibility comes on its own, through stances and through years. Forced stretching before a first class is also the fastest way to injure yourself before you have even started.
The last month before your first class
If you want the most useful preparation in one sentence: every day, ten minutes of supported squats and standing barefoot on one leg. That is all.
And if you do not do that either, come anyway. The first week will hurt the same in both cases - three days in one and four in the other.
