I am assuming you've read the previous articles on energy, elements, and the elemental triplicities. If you haven't, I recommend starting there and coming back.
Fixed fire, leo is the most pure expression of fire energy. I'm going to begin referring to "a leo" as shorthand for someone filled with leo energy, and not in reference to signs in any birth chart.
One of the most common depictions of leo energy is as an artist of some sort, and this does fit. However, it runs the risk of missing the essence of leo and instead providing a checkbox to tick. In Steven Forrest's Book of Fire(I am borrowing heavily from his elements series) he uses the example of a small child on a swingset calling out to her parents "Look at me, look at me!" with a great big smile as her parents watch. Dissecting this scene reveals the anatomy of expression. This young leo had an inner experience, that of riding the swings, and it filled her with excitement. Instead of quietly marveling and meditating on her experience, she reaches out to extend her experience to others. An artist with leo energy does not just paint or sing, but instead invites you to participate in their inner world. This is the nature of expression, which may not only initiate human connection, but may also readily inspire others to express themselves.
"Mom, dad, look....look...I'm....on the swing...." The girl stops swinging and realizes her parents did not even hear her, but talking to a friend that just strolled by. Or perhaps the parents did hear her and gave a half-hearted "That's great" as they played on their phone. Perhaps there will be new moments with the swings, but this one is over. The magic is gone, and so is the joy on the girl's face. These are the stakes with leo. While aries fights to survive and remain dignified, leo fights to be heard and seen, to be connected. Aries energy disregards the odds of survival as it fights for its life. Leo disregards the potential it will be poorly received or ignored. This is the gamble leo makes when it throws back its head and roars, possessing the courage to try. Wounding can easily rob one of leo energy, as a persistent fear or anxiety can lead us to second-guess ourselves and not lean into our authentic voice.
This poor girl sings before a crowd and her voice cracks. She falters for a second, face gripped with anxiety and eyes growing hot. Her gaze snaps desperately to her parents. She sees two proud smiles and can barely make out them mouthing the words "You've got this" with a thumbs-up for emphasis. Re-ignited, she regains her composure and resumes her song despite the mistake. Let's ready our scalpals and dissect this scene. The girl began with leo energy, but it was quickly lost due to anxiety. Anxiety is anathema to leo energy, as it pushes one's focus off of their passion(ie success) and moves to all the negative possibilities(ie failure). A good performance does not require perfection, but instead energy. As she faltered, the girl lost her energy. Note, however, that her parents channeled leo energy and encouraged her, that is, gave her courage. This act of inspiring or encouraging others is an essential application of leo energy. At stadium games, the crowd, bands, and cheerleaders bombard the athletes with leo energy. With this second-hand courage, athletes are able to do what they simply couldn't alone in a silent field.
While a leo's passion may express a wide range of emotions, the vibrancy of enthusiasm behind even their sad expressions is given via a child-like joy. Listen to someone get way too into reciting shakespeare, and you might catch them smiling from how much fun they're having. This is the same joy of the girl on the swings. It is the joy of experiencing something with fresh eyes, of being excited. When a kid descends a slide while laughing, they aren't calculating the odds of landing safely. They're in the moment, feeling a feeling, and enjoying it. When one is gripped with stress during a performance, injecting this child-like joy via a genuine "I'm so excited I get to do this!" pushes away the anxious "I hope I don't mess this up". Remember this when you're channeling your own leo energy and your voice cracks. This is a muscle, and you can strengthen it through practice. Use leo energy's joy to transform work into play. Whistle and dance while you work. Turn it into a game. Mix humor. In a room of strangers anxiously waiting for someone to initiate, break the ice. This is the flame which burns inside a leo and casts warm light in times otherwise characterized by darkness. When the parents look to their girl swinging and shout "I see you, I see you!", this too is leo energy.
One exercise is to tilt your head back, open your mouth as wide as it can go, and breath big breaths through your mouth, letting the air fill your belly instead of your chest. Recall anything that makes you laugh, or listen to a comedian or inspirational speaker. Picture the warmest, most adorable images you can. Remind yourself that your entire life has prepared you for this moment. Consider that 4.3 billion years of star dust and space rocks has lead to this beautiful dance called your life, and that it will never be repeated. Consider that, no matter what happens, this dance belongs to you and you can make it your own.