What are some ways for an amateur boxer to improve their skills without access to coaches? Can they practice at home?

YES! of course there is. back in my day, amateur boxers had a season for tournaments and boxing cards. usually in the fall and winter months. September through April and that when you would train in the gym with your trainers/coach so on the off season the best way to train and learn new things was to watch pro fights on tv and pick up different moves. practice them in front of a mirror or invite your friends over and practice on them. lol. buy a heavy bag and work out on that, keep your cardio going by running/jogging and jumping rope. shadow box and train with weights. back in the day, we were told not to lift weights because it would tighten you up and slow you down but now we all know better. a good weight training program will get you stronger and build your cardio if done right. always train with the mind set that you want to be a champion. stay humble but be positive about your goals. WHAT YOU BELIEVE, YOU CAN ACHIEVE.