For prep, typically the week before my event ill make sure i have everything priced, all my goodies packed up and my tables and extras set aside and packed.
Night before i double check and make sure i have everything ready and load up my car! I leave early so that i have time to grab coffee and breakfast, and then i give myself about a hour of set up time before the event starts!
Also another thing to note is its good to have a way to take credit cards. Square offers a free card swipe reader (they take a like 2.5% fee off every transaction so be sure to build that into your pricing ) Most phones can connect to the reader as it just uses a headphone jack but i actually use my laptop and make it a little like cash register ( I have one of those fancy chromebook laptops that you can flip around and make a tablet tho)