Triggers are everywhere.
From brushing your teeth before going to bed to washing your hands before meals.
A trigger train is a selection of habits that you perform one after the other, resulting in a compounding effect.
How to start
Identify the habits you want to build
Identify a trigger you will link to those habits
Practice
Example
Say you want to improve your presence when entering a room.
Establish the rule that every time you walk through a doorway (any doorway) you straighten up and put a smile on your face.
At first this will seem strange but with time it will become second nature. You will have formed that habit.