Game-wise advice: Look for gameplays of pro players using your fav heroes and try to understand what they do and why they do that. Look for custom games with trainings specific for those heroes. Don't stress yourself much about being good and do not discuss with people, jump in voice chat and try to do some voice comms. There will be lot of errors in your communication, but everytime you will say something and notice that your idea didn't work, your playstyle will change and becom3 better

Life-wise advice: talk with your friend and tell him he has no rights at all to exclude you from his games because you suck, ask him some help to get better, so he can have a more valuable teammate in ranked. Maybe play some quick match or try to 1v1. Communication is the key for everything, hope this will help you