Ok, now it is too late for this one, but there is always the next interview waiting for you.
The most important thing is, to remove EVERYTHING that might be a stress factor or you can't rely on.
First of course the preperation begins at home and i think you already were sure to get the job but one stress factor is of course the questions of the HR department. I for example prepared myself before i even got out my first CV with over 50 potential questions that are common and business specific, the psychology behind it and how to answer (also i trained with a partner and filmed me while doing it to see how i come across). So this wasn't bothering me anymore.
Get your clothes together what you are wearing the day before, so you are not like 5 min. before you go "where is this damn belt" or "damn, there is a stain on my shirt i would have like to wear".
And now to your point: remove 3rd parties as much as you can, that you can't rely on, which includes public transport. The trains can run ALWAYS on time, but the day you are reliant on some idiot decides to kys himself and ruin your day through then a over an hour waiting time the train then have.
So even when you are low on money and don't have a car just go to a rental car service and get one, so you don't have the stress with delayed trains or missed connections. Also watch out for temporary building sites or where there could be traffic jams. Have a backup navigation system with you that might even have traffic updates.
Then make yourself familiar with the place itself, were you will have the interview, beginning looking up google maps to see, where the parking spaces are and were the entrance is (helpful by bigger buildings).
Arrive there to be at least half an hour early, better an hour. So you can take a walk, make yoga or just go to a bakery, get a pastry or sit in a cafe to calm you down and then you go in and be the best foking interviewee they had ever had and crush your competition!