Guatemala is quite traditional, so modest clothing is best. In Antigua there is a lot of tourism and it's a bit more modern, but still, I've read blogs about people being kicked out of cathedral tours for wearing shorts. Women here typically wear long skirts. In the city, you may see more trendy tight fitting pants, but that is not acceptable outside the cities, in villages, etc. I usually wear skirts or jeans that go no higher than about knee length. A lot of websites recommend Khaki shorts (which was also the case in Nepal but few people actually wear that). It might be easier to list what you should NOT wear: Short shorts (anything that shows anatomy, so basically long shorts are ok) Belly tops are a no go Spaghetti strap tops, tight fitting, are a no. Low cut tops are a no. Shorts with bikini top is a no. As you are interacting with local people, it's best to be modest. If you're going to a village, wear a skirt or loose fitting pants and cover chest and shoulder.
Any time you are traveling you are a target for theft of possible violence. When people see tourists, they see $$$ in their eyes. It is common, on the street, to be charged a higher price when you are American, etc., until you become wise of the culture and learn the norms and how to negotiate or have a local person with you. We travel to Guatemala frequently, in cities, in villages and the countryside and have always been met with hospitality. However, you must have your head on a swivel. Be mindful of cash or jewelry, don't pull out a bunch of cash for the world to see. If withdrawing cash from an ATM always close and lock the door. It's not safe to travel with large sums of cash. Don't keep things in your back pockets (like phone or wallet) Use a purse that zips, or is deep, and can be secure on your body (like cross body)
Right now, you have a lower chance of getting measles in Guatemala than the US. However, some forms of Hepatitis, Zika Virus and Dengue Fever are all higher risk there. The biggest risk is stomach bug. Rules of thumb: - Don't drink tap water and be mindful of what you're drinking out of, even at restaurants. Use a straw to drink out of a bottled drink. - Avoid coming into contact with people who have open wounds (I don't know why you would be in contact with that during this trip, but just avoid that). - Use bug repellant with at least 30% DEET. Antigua is in a higher risk area for mosquito transferred diseases due to it's elevation. If you are particularly concerned, immunocompromised or pregnant, you should exercise caution. Higher risk areas would be anywhere with standing water, or natural water sources, forests, etc. The Zip Lining excursion might not be for you. The ATV tour might be one to avoid, if you are concerned.