One of the biggest problems that I see with new playwrights is that they don't really KNOW their characters. Yes, we know characters ultimately are made up, but at least half the time new playwrights don't even based their characters on real people. I AM NOT SAYING that all your characters should be based on real people you know... but it helps, for you often know things about these people that you don't consciously know you know. And that's fun! Those characters pop right off the page.
One of my favorite plays that I have written is called The Eyes of Love (you can find it published on INDIETHEATERNOW.com) and it is the story of a therapist named Mark who falls in love with his client, Annalisa, who is GORGEOUS and NUTS! Right before I wrote it, I was in relationship with a GORGEOUS woman who was also NUTS, and I basically just told our story, only this time I was a therapist and she was my client. I used her stories almost verbatim and I made up other stuff up too but it was congruent with her character for I knew her so well, and not just in the biblical sense. The play was a huge success and it has been produced a number of times because her character POPPED!
So try it. Make everyone in your play someone you know, just change their situation. Even make that bartender character with only one line someone you know, and see what happens. I find when I do this, the dialogue often flows out of me almost by itself as these people I know in this new situation or context, fight, kavetch and struggle for what they so passionately want.
If you know your characters, they will often take on life of their own, AND your play will ROCK!