When you're nervous, your body will kick into overdrive to try to solve the problem itself. You're flooded with adrenaline and your muscles start shaking. To help counteract this, intentionally slow your breathing by inhaling for four seconds, exhaling for four seconds, and repeating.
As science channel DNews explains, your sympathetic nervous system can put your body in a high tension state as soon as you're exposed to a high-stress situation like giving a speech, or a confrontation. While you can't control your body's natural adrenaline response, you can control your breathing.
Most of the time, you're not breathing consciously. However, when you force yourself to do it on purpose, control of your breathing switches to the parasympathetic nervous system, which can help counteract the effects of being nervous.
DNews points to the "combat tactical breathing" technique used by the military as an effective way to control this. Simply put, combat breathing involves counting to four for each step of the breathing process. Breath in, count to four. Hold your breath, count to four. Exhale, count to four. This process can act as a soft reset for your nervous system and calm the shakes faster.