If you are going to Japan as your first trip to a foreign country, my guess is you're going to try to do touristy stuff and not try to "have experiences". I'll base my answer on that, and restrict everything else I'm saying to what you can expect to find in large cities. Be aware that if you go to small towns, the following information may not be correct.
It's pretty easy to get around in Japan without Japanese, as long as you speak English and you don't need to talk to anyone. Japanese people speak English pretty poorly overall, so trying to ask for anything complicated may land you in trouble. However, all signage in Japan is bilingual in English, so finding directions around the train station, or finding a washroom, or reading (most) maps should be fairly easy. Many restaurants have English menus as well, at least the larger chains, so finding decent food should not be hard either. A note about ordering food in Japan is that it is quite common for foreigners to point at what they want on a menu, so don't be afraid to just point at what you want instead of trying to pronounce it poorly.
In general, you will want a smartphone with an internet connection much more than you'll want to be able to talk to people. Japanese geography is quite confusing, so knowing how to get from point A to point B is important. You can buy a travel SIM card from the larger electronics store chains and also some convenience stores, which should last most of your trip (don't watch YouTube on it though, or you'll find yourself losing valuable data quickly!). My recommendation is to not buy it at the airport from the SIM vendors there; they tend to be very expensive and you can find one for half the price at a store in the city. Once you have that, Google Maps is your best friend, both for foot travel as well as train travel; Google Maps has really good accuracy with Japanese trains. Don't take taxis in Japan; they are very expensive and not particularly more efficient than the train in terms of travel time if you have Google Maps to guide you when to switch trains and so on.
Most Japanese people are pretty understanding of foreigners who don't know Japanese, and they'll do your best to help you out when you're stuck. That said, be aware that they mostly do not actually speak English (not well, anyway), so don't try to ask them for anything complicated or you'll wind up with a ?????? look and no progress. However, they do mean well, so don't be afraid to ask for help if you need it, the same way as you would in your own country.
As for staying out of dangerous situations, there is no such thing as danger in Japan. The crime rate in Japan is extremely low, and you will be 100% safe at any time of day, anywhere in the country, by yourself or in a group. Don't worry about getting randomly mugged in a dark alley or whatever, that sort of thing simply doesn't happen in Japan. Don't worry about carrying large sums of money on you if you think you may need it for some reason; you won't get robbed, and if you do drop your wallet by accident it's more likely for someone to return it, with the cash still intact, than for someone to make off with it. As a Westerner, this concept is fairly foreign to someone who hasn't been to Japan, but really I mean it, you are safer in Japan than probably anywhere else in the world. Just don't talk to anyone wearing a suit in Kabukicho, that's the main way to get yourself in trouble if you don't know what you're doing.