Tips about Guatemala:
1) Don't eat the black beans. Seriously.
2) Don't drink the water, or drinks made from water that is not sterilized.
3) Take anti-diarrhea medicine in your bag, along with pepto bismol, and any other medicine that would help with upset stomachs.
4) Eat what you're served. Don't be rude and be picky about the food. It's a once in a lifetime experience. Enjoy it. As I always tell my daughter, "try it, you'll like it!" Ok, this may not be true (I tried some pretty nasty things), but trying it and not liking it is much more respectful than refusing to eat, and demanding "American" cuisine.
5) Don't go to McDonalds. Just don't do it.
Your fancy schmancy iPhone will not work in Guatemala. Don't bother. If you really, desperately need a phone, then you can buy a cheap one through the local cell phone company. I chose to do this so that if my daughter needed to get ahold of me for any reason, I could be reachable. Offhand I do not remember how much I paid, but it was very reasonable, less than $50 for the phone and minutes. I would not recommend trying to get a phone if you do not speak Spanish, or have someone to help you buy it. Honestly, once I got used to not sending a bunch of random texts like I do at home, I didn't miss the phone. There's always the internet to keep in contact.
Best bet, avoid standing out. If you are like me, tall, blond, and blue eyes, you'll already be the obligatory sore thumb. Dress conservatively. Guatemalans do not typically wear shorts. Especially not short shorts. Basically anything that shows legs or cleavage is a no-no. Do not wear flashy clothes/jewelry/bags, etc. Don't even take your diamond rings. Leave them in the states. This should be an obvious one, but people still did it. Your D&G purse will be slashed way before my plain black Wal-Mart purse. Thieves and robbers are much more open in Guatemala-it's not really hidden. Be aware of your surroundings. They may come up to the car window and demand your stuff while wielding a gun (it happened to one in our group), your purse may be slashed without your knowledge, leaving all the contents to spill on the ground. They may climb aboard a bus and demand belongings while holding up the driver. Just be aware at all times.