There will come a point when there is a shift in your audience's reaction. It will go from a polite, respectful applause to a rousing, enthusiastic, fervent one. Your friends will compliment you with a hint of disbelief in their voice and people you don't know will start coming up to you gushing about your show. People (if you do it right) will start coming back to your shows and bringing friends. At some point you will look out at the crowd and there will be more faces you don't recognize than those you do. That will be the moment you know your're on to something.
Once people start requesting to book you, you need to know what (and if) to charge. Obviously, you can do benefit concerts for free if you believe in the in the cause, But always ask for a "stipend" to at least cover your expenses. Or charge them a very reduced rate. And make sure the gig will represent you well and will cover all of your necessary technical requirements . You don't want to take a benefit concert only to find out that you're going to be playing in the corner of the cafeteria, without a stage, through a sound system that only half works, with one mic on a shaky stand. Or worse a completely "unlit stage". So if you take a gig send your tech rider and compromise on less.
How To Make It In The New Music Business - Ari Herstand