Stage presence is a complicated thing, if only because it comes in so many varieties. If we were to compile a list of guitarists considered to have a great stage presence, we would probably find that no two are quite alike.
Let's start with the fundamentals - stage presence is the conveyance of feeling comfortable on stage and complementing your musical performance with the appropriate visual aspect.
'Appropriate' is a key word here. What will be considered appropriate depends on the music being performed. While a swing guitarist playing his ES-175 behind his head might get a few laughs these days, rather than being subject to horrified looks from the audience as would probably have been the case only a couple of decades ago, some forms of showmanship fit better with certain musical styles than others. Thus, a lot of what consitutes a good stage presence will be dependent on the genre in question.
There are some things common to just about any genre and this is what I want to focus on.
1. The appearance of confidence
This is stage presence at its most basic. Playing live consists of brief moments of bliss between problems of all stripes - from bad stage sound, through technical glitches, to moments of brain-freeze where you forget what you were supposed to be playing. Preparation can avert the most typical problems, but new ones will always materialise. It's simply part of the game.
Whatever problems we encounter, however, we must at all times endeavour to keep our composure and keep the audience unaware that something is wrong. They came to have a good time, after all. The most valuable skill a performing musician can learn is the art of quick recovery, followed closely by putting on a good face in a bad situation.
Confidence consists in knowing what you are playing, what you are supposed to be doing at various parts in the show (this may be as simple as "What is the next song on the list?" or as complex as a series of pre-choreographed movements, keyed to music and lights) and what you will do if something bad happens. Even if at some point you don't quite feel confident about any of those things, you must at least look like you're in control.
2. Situational awareness
When playing live you will be playing for other people and very likely with other people. Live music is a shared experience and conscious participation requires you are aware of what's happening around you.
A lot of beginning performers are so focused on getting their part right that they switch off as much of the on-stage environment as they can. In the worst case scenario, they might actually drift out of time, because they weren't listening to their bandmates. However, a musician that lurks in his corner of the stage, never lifiting his eyes from his instrument, is almost as bad.
You should have your parts down well enough that you can actually cast a glance around you. Situational awareness allows you to interact with the other musicians and with the audience. See that guy playing air guitar in the first row? Why not play up to him? Have a bunch of accents played in unison with the drums? Get up close and really play together. Are you playing lead under a vocal line? Why not lean in with the vocalist for that part? These are all rock cliches, I admit, but they're supposed to illustrate a thought process.
3. If you aren't enjoying yourself, the audience probably won't either
One point I always try to put across is that the live performer is in the business of providing entertainment. This means that you must avoid sending out bad vibes to the audience at all costs.
Now, we should quickly specify that what's at issue here are bad vibes about the gig. An aggressive, politicised punk or metal band may be expected to vent a lot of negative feelings about whatever gets their pressure up - the audience will be expecting this (hopefully). However, whatever personal, technical or reception problems we might have (sometimes the audience simply isn't buying us), we cannot let our negative feelings show.
Sometimes, this may mean putting on a fake smile, but it's something we owe our audience.
4. Develop your own onstage personality
We aren't actors, but our stage personna is an act to some extent. We remember Hendrix as the teeth-picking, guitar-burning, spaced-out Guitar God, but we'd be foolish to think that this describes him off-stage. The iconography remains, but we have to concede it shows only a small part of Hendrix the man.
Think about yourself as a person, yourself as a musician and yourself as a guitarist. Are you introverted or extraverted? Physical or cerebral? Emotional or rational? Are you a flashy, technical player or rather a melodic type, whose sound is all about feel? Or maybe you just like to rock out? Focus on the stuff that comes naturally and you'll find developing your onstage personna much easier.
5. See as many live performances as you can
I purposely avoid making any recommendations, since they are bound to be genre-specific and somewhat subjective. Moreover, any such list is bound to be incomplete.
Instead, here are some suggestions of what to look out for:
What is the impression you get from watching the musician in question? (You should be looking at all of them, not just the guitarists.)
Do you think it's appropriate/effective, given the music and the overall show?
How do the musicians interact with each other?
How do they interact with the audience?
How do they start and finish their songs? How do they develop them and what nuances of performance and showmanship do they use in key spots?
How is the setlist constructed? How do the musicians go from one song to the next? What's the flow of the show like? Do you think it's effective?
Note: You should pay particular attention to the beginnings and endings - in terms of both individual songs and the show itself. The start and finish are the most crucial elements. To quote Keith Moon: "They remember your entrance and your exit. The rest, in the middle, don't mean a goddamn thing."
6. Try to record videos of your own performances
For all our best intentions, we cannot see ourselves with the eyes of the audience until we put ourselves in the audience. Videos of your shows are to your performance what recording is to your playing.
Watching yourself on stage may be uncomfortable at first, but it offers great rewards in terms of critical evaluation. Use the same criteria as for reviewing other people's performance and look to improve those spots where you find yourself wanting.
Above all, have fun!