Prepare names for the 拝見, don't forget to ask about the tea.
茶実
Clean the 畳 with a dry towel, folding it over every 畳 length
炭
Preparation of the 灰型 can happen the night before, but the ☵ is only written just before the coal is laid, to allow more air in. Also, フジ灰 you add then, too.
You should also have a back-up 釜 running, so in case something happens with the fire, you still got boiling water. In that case, you'd use straw ash (わら灰).
Fill in the coals as if they were growing from the ground; so you can check for branch holes, or just see which side is thicker (= bottom).
えだ炭: try picking them up.
Rattle it slightly to see if the coals hold.
はいき: Don't tap the spoon on it, since it is quite fragile.
茶碗
Practise cleaning once if it's a new bowl
茶入
See that 茶杓 can rest on the lid
Make sure knot is loose enough
Check what's a good distance from the 水指 so that the 茶杓 will be only a hair's breadth away from it.
棗
Check front
In III 20, I found it nice if there's the slightest dust of tea powder on the 棗 which can then be dusted off