"You get a deeper and more forceful breath, and it helps with your chakra circulation." Deep breathing was a good thing to practice anyway, as was almost religious stretching routines to unkink everything that got kinked when bouncing off ceilings and slamming into walls.

"Now...the most important thing in a fire jutsu isn't the heat or the distance, but being able to balance control with power. Fire is, in its nature, destructive and greedy, so as long as your provide it with fuel it will damage and kill. In a place like Konoha, and when in a fight with allies, fire can be more detrimental than anything else. You should always focus more on control in a fire jutsu and know your limits. Duration is also important. Hair will catch fire quickly, and skin burns easily, but most clothing takes a few second longer to catch, or a hotter flame." Itachi realized he was rambling. As fire jutsu were one of his clan's trademarks, he'd grown up hearing discussions on them and could get carried away.

"It's mostly practice and observation, which are unfortunately things you have to do for yourself." Which made Itachi a rather ineffective teacher. Go forth and burn things and call it training. "Sorry, I'm not very much help."