Bring as much cash with you as you can, in clean, crisp, unblemished 100 dollar bills of the latest series. When I came in 2014, the limit before having to declare it was 10K. Obviously, spend what you must for a decent quality money belt to wear under your clothes.
Learn the difference between the official exchange rate and the "blue" rate. Don't pay in dollars and get ripped off with the official rate. Learn Florida street and find a cueva you like.
Don't bring an expensive iPhone and flash it around in public; thieves will snatch it right out of your hand. Learn to carry your wallet in a front pocket of your pants, not in the hip pocket as we do in the USA.
Be wary of buying anything from street vendors.
Learn about futból, what is called soccer in the USA, or you won't be able to make small talk.
Be prepared for the fact that the local Spanish is very different from that of Mexico. There are different names for everything, a different pronoun for second-person singular informal, and a new verb form for that pronoun. The Y sound, whether from an actual Y or a double-L is pronounced as an SH, (or sometimes more like a ZH, in those upper-class people who went to a fancy school).
Make an effort to learn the metric system. You will be glad you did.
Cultivate patience, and philosophical acceptance of broken plans, or Argentina will drive you crazy. Expect people to be half an hour late for appointments and agreed meetings.
Be prepared for disappointment on the subject of coffee. There are only two choices. There is Brazilian coffee, which is cheap and ubiquitous, but tastes like muddy goat piss. From a diseased goat with bad kidneys. Or there is Colombian coffee, which is the divine elixir of the gods, but hellishly expensive.
If you like to burn rope, be prepared for disappointment. The good stuff is unobtainium here. There are no dispensaries like in California, and it's still illegal.
The red wine is very good to excellent, but the white is mostly undrinkable; it's sweet as pancake syrup. Others can give you better guidance on this subject. I have only a waiter's knowledge of wine, and I'm from California, where the default is a Chardonnay almost as dry as vinegar. User The Rich One is our local gourmet/gourmand, and his advice is always impeccably good on anything to do with food or wine.
Don't eat the seafood here in Buenos Aires, and for the love of GOD don't eat shrimp. The beef is excellent, and cheap. The pork is great if it's fresh.
Stay strictly out of all political discussions until you have at least 2 years in-country. There are no direct parallels between US politics and those of Argentina. Its all different. Kirchneristas are not Democrats, and the PRO/Cambiemos are not Republicans. Peronism is neither of the Left nor of the Right. Cristina is not the devil, nor is she guilty of all the things of which she is accused, but you would think both of those things from some comments here on these forums. Then again, she is damn sure not a saint; she's a politician, with "feet of clay" up to her cooter.
Last but by no means least, welcome to Argentina. Contrary to the naysayers' pessimism, you can be very happy here. You can learn to love Argentina. Just be aware that somewhere around the 90 day mark in-country, you may suffer a psychological crisis of sorts, when the homesickness is all but unbearable, and the problems here seem insurmountable. Tough it out and it will pass in 3 days or less. Don't give up and leave in the throes of that very-temporary despair. This is a wonderful country with many excellent advantages, not least of all a very low cost of living. You just need to accept that some things will never be like they are in the USA. There is no bacon, and there is no Charmin.
All of the above is just my opinion, and many here will substantially disagree.