This primarily comes from a full understanding of your character’s normal and special moves. Hell, just run through the game and experiment with your normal moves. Just by looking at its speed and range, you can get an idea for how Gen is able to control and dominate space. Look at his jump-arc, and how his jump attacks are able to cross-up and not cross-up. You can use this to great effect in your offense, since his jump is so quick and travels in a short arc, you’re able to catch people off guard if they’re not ready for it.
You have to remember that a “fireball” is just a temporary extension of character’s attack range. It’s part of that character’s footsies as well. The same goes for your normal moves, such as the hand slap, and wall dives.
This isn’t something you’re going to learn by watching a tutorial guide, you’re going to have to put in serious work in your character, either in training mode or in live matches, to get a strong feel for your character. This means learning which normals and specials to use, why you’re using it, how effectively you’re using it, and more importantly, how risky that move is.