I have a bit of a different view. Stage presence does not come naturally, rather those who seem to have a "natural" presence learned so early that it appears natural even to them.
I agree with what's been said about confidence. You can even tell the difference between two very stunning technical dancers--the one who's done it a thousand times and comes with all the unspoken confidence of that experience is quite obvious; whereas someone who is "adopting the pose," however good the pose is, will also be very clear.
That confidence comes from a very clear intention--you know what you're about to do in a dance. What's more, you know that you have a number of different steps you can use--and you don't necessarily know which ones you'll use at any given moment. But you're alive in the moment and you know that you'll choose something from your arsenal. That is vey different from having a rigid and inflexible choreography. You can tell who dances according to pretty strict choreography, and who is comfortable making it up--even if they're not making it up at the moment. The awareness that things can change at any moment will affect even the choreographed sequences.
Your intention is clear in terms of two things--your relationship to your partner, and your relationship to the audience. If you're responsive, that will appear in a better sense of presence. If you're inwardly focused, maybe thinking hard about how to execute a step, then that will read too.
Presence on stage of any sort is a matter of attention directed outward, an awareness of partners, audience, space, energy, everything. That's why I feel that practice is the time to focus on technique and performance is the time to forget about it--not because technique isn't critical, but because it should be internal. There's nothing worse, in my view, than watching a couple practice when they should be performing.
So my suggestion to work on presence would be to forget all the technical things and be awake and alive to the moment.
A simple acting exercise can get you in touch with the world outside. Do a little mirror game with your partner. First your partner does something, and you try to mirror him. Then you do something, and he mirrors you. Next he starts again, and at a particular period (usually when you coach or your director tells you to), you take over and your partner follows you. And then, you try to establish a rhythm where you naturally shift back and forth--you're doing the exercise well if you can't tell where one person stops and the next starts.
And ask yourself why you're dancing this particular dance with this partner. Even before the dance starts--gentlemen, why do you even extend your hand to this lady? What are you asking? Ladies, what are you answering when you approach? If you can't answer those simple questions, IMO, you have no business dancing--however flawless your technique. You don't have to verbalize your answers, but you need to have the answers in the form of at least an unspoken relationship.
When your partner turns you out, or when he lifts you, what's going on?
That kind of presence isn't something that you have. It's something that you give.
Hope this is all at least semi-lucid!
Cheers,
Genesius