Guatemalan men are often dominated by a *machismo* mindset and can be chauvinistic. Solo female travelers may recieve unwanted attention in the form of catcalls, horn honking, and whistling. The best tactic is to simply ignore this. As a preventative measure, it's a good idea to dress conservatively and try to stick to the main tourist destinations.
Guatemala also has tons of foreign visitors, so it isn't necessary to travel alone if you don't want to — it's easy to make friends at hostels, hotels, restaurants, and bars. Take cabs after dark whenever possible.