I probably make shit coffee but from what I understand, you are supposed to open it only a fraction of the way. When it's completely open, it forces it through the filter and that's what makes it bitter.
I fill it to the brim and let it steep for 4 minutes, then slowly draw it out over 30-45 seconds. I try to hit the spot where I'm barely lifting the ball up.
I also heard stirring it help (both when you first put the liquid and then before draw).