I've travelled from Chicago to the UK; I've also honeymooned in NYC; I've never been to Cali: So here's what I can share with you:
In NYC
-just called it "New York" not "NYC" or "New York City." People in NYC like to think as their city as plain old "New York." It's weird, but to call it anything else marks you as an outsider. Oh, and the phrase, "Big Apple" doesn't really make it round well in common conversation in NYC.
-never take out your wallet: Carry your big bills or credit in your wallet, and use small bills from your pocket or bag to pay for everything. Basically, never make it apparent that you have a lot of money on you; if you have to, keep it different spots (heh, my grandfather, back in the day, used to tie it to his thigh, but he was a boss, ya know? Haha).
-try not to talk to strangers; I get it that you might get lost, and need help, but ask a worker of some kind (police, bus, train); try not to talk to the homeless (it's actually dangerous, despite a philopatric heart) and really, don't even talk to the people passing you by on the street; everyone is in a rush and has somewhere to go, and you'll be lucky to make eye contact with anyone, honestly.
-find your scene, and enjoy it. We happened to have spent our honeymoon in Park Slope, Brooklyn, a really safe and hip area; we were blessed that my husband's cousin lives there, and had our own personal tour guide: We saw cool thrift stores, nice coffee shops (albeit tiny and expensive), had bagels and pizzas delivered to our door (at separate times), and even jammed at Jurassic Park Slope Studios (they even had a set of bongos for me, and a Les Paul for my husband).
In America in General
-If you don't have to eat corporate food, then don't. Try to find local places, like "mom n pop" shops, where the owner is the sole proprietor; avoid McDeath (McDonalds), Booger Fling (Burger King) , and all the others. Chances are, if you've heard of the place before, don't eat there.
-before you leave, make sure your mobile phone will work in the USA (when I went to the UK, I didn't check this, and couldn't even tell the time, bc i hadn't even packed so much as a watch). Call your provider, and even check data prices; at a lot of places in the US, you can pick up wifi (wireless internet) and should be able to operate your phone for a cheaper rate.
-also, for america, download apps for your phone like YELP and Google Maps; these two are great devices and will help you find just about everything you need. YELP is used to find stores and restaurants, while the Google Maps will locate anything, and give you directions in either walking, public transit, or personal vehicle.
(TO ANSWER YOUR QUESTIONS)
-If you get hurt, you go to the ER (emergency room) of a hospital; as of right now, they can't turn you away; they can just charge you up the *beep* later on. So, PLEASE DO NOT GET HURT!!! Again, if your mobile works, just dial 911 anywhere in the USA and help with assist you.
-uh, tipping... Well, if your service is horrible, I suggest you tell a manager, and specify that your tip is not for the service, but for the chefs or the restaurant in some way. Usually, I like to leave big tips if possible, like at a diner where the check is $20, I would tip $5, but I used to be a waitress, and am a bit generous to their plight.
-transportation varies from location to location within the USA. Hopefully, if you're in bigger cities, you can always rely on either your own two feet, bus, cab, or train. Albeit, if you're going anywhere rural, you might want to rent a car; but that is a difficult procedure (must be at least 25, w/ credit card, and insurance, blah blah blah).
-Phrases? Hm, Wouldn't worry to much about that. One thing most Americans love is a cool accent. So speak your normal way, and I'm sure someone will overhear your conversation tone, be intrigued, and strike up a conversation with you.
-I suppose, finally, just don't be naive; try not to trust openly, don't follow anyone into strange looking deserted areas; but hey, also, HAVE FUN. Enjoy your trip. Take photos. And Have a blast!
