Study those who have a natural charisma and presence in any situation, and watch what they do. This can help you pinpoint the things that you aren't doing that you should to have a good stage presence.
Rehearse and prepare for the role more than you think you should. Nervousness and jittery performances will take away from the presence you have on stage. Have a good stage presence by being so prepared that you can give an effortless performance every time.
Warm up well before the curtain comes up. This can be done with vocal warm ups, running or jogging in place or running lines with your fellow cast members. You'll have a good stage presence if you come onto the stage fully in character and warm.
Have confidence in yourself and your talent. It is easier said than done, but just fake it until you make it if it doesn't come naturally. This doesn't mean you should walk around like you own the place, but just tell yourself that you are confident and talented until you believe it.
Smile with your entire face. It may sound silly, but those with a good stage presence usually appear very open and free. This means ditching the fake smiles for the stage and adopting the most naturally free and open smile you have.
Compel the audience by being absolutely still, and by only moving when you must. Excessive head bobbing and gesturing will dissipate any tension you have built in your performance. Let the words speak for you, and gesture and move only when necessary.