Prepare your stage banter. During band rehearsals, run through the bits between songs. It's surprisingly difficult to think of something to say to a room full of people if you haven't prepared. One of your roles as frontman is to engage with the audience. Write down which songs you are going to introduce and include a note in your set list. This gives your band a chance to tune up while you talk to the audience. Don't introduce every song, as this will break up the flow of your set. If you have a show booked, think of something topical to say about the town beforehand. Alice Cooper has a member of his crew purchase a local paper before every show. He picks a story and makes a short reference to it during the show.
Rehearse in front of a mirror. Stand a full-length mirror at one end of your rehearsal room. When practicing, perform to yourself. Observe your gestures and movements. After each song, make a note of what worked and what didn't work. Don't do anything that makes you feel uncomfortable. Trent Reznor cuts a very impressive figure as a frontman doing very little. If "mean and moody" is your thing, go with it.
Organize a series of hand-signals that you and your band can use to communicate. For example, tell your drummer to count-in when your raise your left hand. This prevents the band kicking in before you're ready.
Handling mishaps in a discreet manner is key to being a good frontman. If you miss your cue, don't stop the song. Signal to the rest of the band the amount of bars you want them to play before you come in again. If you make an obvious mistake, like dropping your tambourine, act like you meant it. Don't quickly reach down to pick it up, leave it there and get it when the lights go down.
Make regular eye-contact with the audience. Don't stare them down, but deliver key lines with conviction. It's hard to engage with an audience if your eyes are constantly on the floor. Pick a few lines in each song where you look to the audience.
Avoid the audience pre-show. In smaller venues, there are no dressing rooms. If you're hanging out in the bar before the show, you limit your mystique. People have already seen you. Wait in the van or go for a bite to eat before stage time. Take to the stage only when the band is ready. Any "cool" you have will quickly diminish if the audience sees you standing about on stage waiting for the guitarist to tune up.