If you've done it before, what are you nervous about? Just arrive a bit early, wash your hands, work clean and neat. do what you are told and work to the best of your ability. Ask what you can do next. Stay as long as you can.
staying as long as you can is terrible advice. if you got the job you would know around the half way, three quarters mark. sticking around looking useless is never a good look. just saying.
i wouldnt sweat it. if you dont get the job, im sure some other chef who is just as good or better will give you one. but in my opinion, if you were really after it you need to walk a tight balance between asking enough SMART questions (ie: "how many covers do you do?", "how does the chef interact with the rest of the cooks?, "what time do you usually start if your in the juice?"), and showing that you ready, capable for the job, nobody wants to hire an idiot regardless of how eager they are. when service starts, you need to be active. plating, cooking, whatever, dont be picking herbs all day thats for amateurs who dont get the job. make sure you are tasting the food, no questions asked it should be second nature. show that you can stand up to the other cooks, that you are the same level as they are or better. but honestly, stage at 2-3 restaurants at a time, just to have a backup plan.