Its normally quite simple, if people sub or like your videos and give positive responses then you cant be that bad. However if you have been doing it for a while and you dont tend to grow atall then your probably not very interesting and need a change. If your on twitch if you see people click on and then back off your video straight away then its again a bad sign. As a small channel its hard to start off and know if your any good or not but after a little while you will get the idea.