A Cue is the most important part of a habit. It is what triggers the habit loop.
The first step in diagnosing a habit is to be aware that you are in the habit execution phase. e.g. While brushing your teeth, while munching on your afternoon snack etc.
The second step is to see if you can take a pause or slow down. For example, if you are brushing slowly stop brushing and look at yourself in the mirror. Be aware of the brush in your hand, the paste in your mouth.
The third step is to ask the following series of questions :
This is the most important awareness to start building good habits or breaking down bad habits. See the diagram below to see the areas of awareness :